Thanks for being here and getting started with Atomico. Let's talk a little about what Atomico offers today:

1. Development agility, Atomico's functional approach simplifies code at all stages of development.

2. Lightweight inside and out, Atomico allows you to create a component with less code and with a low dependency impact. Approximately 3kb.

3. Really fast, Atomico has a good performance in the browser and an agile development experience. Let's understand what a webcomponent created with Atomico looks like:

// IMPORT
import { c, html, css } from "atomico";

// WEBCOMPONENT
function component({ message }) {
  return <host shadowDom>${message}</host>;
}

// WEBCOMPONENT PROPERTIES AND ATTRIBUTES
component.props = {
  message: String,
};

// WEBCOMPONENT APPEARANCE
component.styles = css`
  :host {
    font-size: 30px;
  }
`;

// DEFINITION OF THE WEBCOMPONENT AS A TAG
customElements.define("my-component", c(component));

// IMPORT
import { c, html, css } from "atomico";

// WEBCOMPONENT
function component({ message }) {
  return html`<host shadowDom>${message}</host>`;
}

// WEBCOMPONENT PROPERTIES AND ATTRIBUTES
component.props = {
  message: String,
};

// WEBCOMPONENT APPEARANCE
component.styles = css`
  :host {
    font-size: 30px;
  }
`;

// DEFINITION OF THE WEBCOMPONENT AS A TAG
customElements.define("my-component", c(component));

Let's analyze the code in parts ...

Import

import { c, html, css } from "atomico";

What have we imported?

1. c: Function that transforms the functional component into a standard customElement.

2. html: Function to declare the template of our component, you can also use JSX.

3. css: Function that allows creating the CSSStyleSheet (CSS) for our component as long as it declares the shadowDom.

Webcomponent

function component({ message }) {
  return <host shadowDom>${message}</host>;
}

function component({ message }) {
  return html`<host shadowDom>${message}</host>`;
}

Our component function receives all the props (Properties and Attributes) declared in component.props, the component function declares all the logic and template of the webcomponent. An important rule within Atomico is "every component created with Atomico must always return the tag".

Reactive properties and attributes of the webcomponent

Atomico detects the prop (Properties and Attributes) of the component thanks to the association of the props object, this through the use of index and value allows you to define:

1. index: Name of the property and attribute.

2. value: type of the prop.

component.props = {
  message: String,
};

From the example we can infer that Atomico will create in our webcomponent a property and attribute called message and this can only receive values of the String type.

Appearance of the webcomponent.

Atomico detects the static styles of your component thanks to the association of the styles property:

component.styles = css`
  :host {
    font-size: 30px;
  }
`;

styles accepts individual or list CSSStyleSheet (CSS) values, the return from the css function is a standard CSSStyleSheet, so it can be shared outside of Atomico.

Definition of your webcomponent

customElements.define("my-component", c(component));

To create our standard customElement we will have to deliver our functional component to the c function of the Atomico module, the c function will generate as a return a customElement that can be defined or extended.

Example

Creating sites with Atomico is really easy and SEO friendly because:

1. With Atomico you can perform SSR and SSG thanks to tools like Astro build, with Astro + Atomico you can send previously rendered components to the client, thus giving a result at the HTML level that is really friendly with search engines.

2. Atomico being really small (3kB) your sites will load fast, especially if you only apply SSG with Atomico.

3. Atomico not only supports SSR through Astro, you can SSR today with Atomico in Next.js, Express or any environment that supports ESM modules.

4. (Coming soon) Yes, with Atomico soon you will be able to create blocks for Gutenberg easily

We recommend for SSR or SSG based sites

we recommend you for new projects

We recommend the use of Astro build with the @atomico/astro plugin, with this you can create sites like atomicojs.dev

we recommend you for projects based on React

Preferably we recommend Astro + React + Atomico, but in case your project inherits the use of Next.js you can do SSR with Atomico in Next.js using @atomico/react.

import { c } from "atomico"; // 2.5kB

const MyComponent = c(
  ()=><host shadowDom>Hello, {name}</host>,
  {
    props: { name: String }
  }
);

customElements.define("my-component", c(component));

import { Props, c } from "atomico"; // 2.5kB

function component({ name }:Props<typeof component.props>) {
  return <host shadowDom>Hello, {name}</host>;
}

component.props = {
  name: String,
};

customElements.define("my-component", c(component));

import { c, html } from "atomico"; // 3.0kB


function component({ name }) {
  return html`<host shadowDom>Hello, ${name}</host>`;
}

component.props = {
  name: String,
};

customElements.define("my-component", c(component));

import { c, html } from "https://unpkg.com/atomico"; // 4.0kB


function component({ name }) {
  return html`<host shadowDom>Hello, ${name}</host>`;
}

component.props = {
  name: String,
};

customElements.define("my-component", c(component));

Atomico simplifies learning, workflow and maintenance when creating webcomponents and achieves it with:

1. Scalable and reusable interfaces: with Atomico the code is simpler and you can apply practices that facilitate the reuse of your code.

2. Open communication: with Atomico you can communicate states by events, properties or methods.

3. Agnostic: your custom Element will work in any web-compatible library, eg React, Vue, Svelte or Angular.

4. Performance: Atomico has a comparative performance at Svelte levels, winning the third position in performance according to webcomponents.dev in a comparison of 55 libraries among which is React, Vue, Stencil and Lit.

API

Special properties

render

By default, the render is configured to be used within the webcomponent by reading the return of the function, but it can be used outside of Atomico, example:

Constructor with custom element

This technique allows you to use any registered custom element without the need to know its tag-name for its use, example:

Advantage :

1. Remove leverage from tag-name

2. Infer the types of the props and autocomplete only if you use JSX and Atomico.

Constructor with DOM

Atomico allows the use of the DOM, for this it establishes its created or recovered node as a constructor, example:

Dynamic constructor

Atomico associates the variable associated with the instance as a constructor, example:

staticNode

allows to declare a node within the scope of the function as static, this will optimize the diff process between render, achieving better performance in cases of high stress of the UI, example:

the biggest advantage of this is that the node accesses the scope of the webcomponent

cloneNode

Allows to clone a node from the virtualDOM, example:

The objective of this feature is to retrieve slot and use it as a template from the webcomponent.

SSR hydration

Atomico allows reusing existing DOM in the document. This is done during the webcomponent instatiation, by setting a special property in the tag to mark it for hydration.

This can be done for shadowDom too:

Class name inheritance

Atomic creates a customElement from a function, Atomico will take the name of the function and associate it as the name of the CustomElement in CamelCase format, example:

This results in the class name being equal to Button. This feature is useful for tools like Storybook, when serializing the JSX.

How to declare a component?

Atomico, like React, allows a declaration of components using only functions, example:

From the example we will highlight the following differences:

1. In Atomico you only use one import.

2. useProp is like useState, but with the difference that useProp references the state from the webcomponent property defined in counter.props.

3. counter.props allows us to create the properties of our webcomponent, these are like React's propTypes, but with a big difference they are associated with the instance and can be read and modified by referencing the node, example document.querySelector("my-counter").count = 10;

4. ReactDom.render needs a reference to mount the component, in Atomico you only need to create the my-counter tag to create a new instance of the component.

5. The <host/> tag is similar to <> </> for React, but <host/> represents the webcomponent instance and every component created with Atomico must return the host tag

6. This is only readability, but in Atomico by convention we do not use capital letters when naming our component, these are only used when creating the customElement as in line 16, since Counter is instantiable.

Now I want to invite you to learn how to declare a style using Atomico.

How do you declare styles using Atomico?

It is common to see the use of libraries such as Emotion or styled-components to encapsulate styles in React, but these add an additional cost, be it for performance or bundle, in Atomico there is no such cost.

Instances, children and slots

It is normal for React to create components that you then instantiate within other components, for example:

with Atomico there are certain differences:

1. With Atomico you can instantiate CustomElements using its constructor

The constructor in Atomic is the product of the c function and is the one you will use to register your webcomponent, example:

According to the previous example, you can instantiate MyComponent as a JSX Component, example:

This instance type allows autocompletion at the JSX level and type validation at the Typescript level.

2. With Atomico you can instantiate components as functions as long as these are only stateless functions

This will be useful for reusing templates, but always remember stateless.

Many teams decide to use Atomico for the development of their design systems thanks to its similarity with React, which greatly facilitates the incorporation of human talent into the development of design systems.

Why use Atomico to create design systems?

Use cases

IBM IX

We thank IBM IX since they have shared their experience in the development of the design system for their client Barmer, you can follow this case through Discord or Github.

Props is the Atomico recommended way to declare visible and accessible states at the instance level of your webcomponents, with props you can:

1. Access state via instance, example: document.querySelector("my-component").myStateProp.

2. Dispatch events on prop value change, example: document.querySelector("my-component").addEventListener("myPropChange",console.log).

3. Reflect attributes as prop, example: <my-component my-prop="...."> to document.querySelector("my-component").myProp.

4. define strict input types for props.

Syntax

Any function that represents the webcomponent will be able to associate the static object props for the declaration of reactive properties and attributes, for example:

Consider that:

1. The prop names in Camel Case format will be translated to for use as an attribute to the Kebab Case format, this behavior can be modified through the "attr" property when using a structured declaration.

2. Structured declarations require the "type" property minimally.

3. Not all types can use the "reflect" properties.

4. The declaration of the "value" property can vary depending on the type.

Simple statements

Simple statements allow setting just type validations.

Structured declaration

Improve the definition by adding utility declarations, allowing for example to reflect the property's value as attributes, automatically emit events or associate default values. Remember these types of declarations minimally require the use of the type property.

Prop.type

Prop.reflect

If the "reflect" property is set to true, its value is reflected as an attribute of the webcomponent, this is useful for the declaration of CSS states, example:

Prop.event

It allows dispatching an automatic event before the prop value change, example:

Where:

• event.type: String - optional, name of the event to be emitted when the prop is changed

• event.bubbles: Boolean - optional, indicates that the event can be listened to by containers.

• event.detail: Any - optional, allows to attach a custom detail for the event

• event.cancelable: Boolean - optional, indicates that the event can be canceled by any listener

• event.composed: Boolean - optional, allows the event to exceed the shadow-root limit

Prop.value

Atomico allows the definition of default values of the props.

The association of callback as value allows generating unique values for each instance of the webcomponent, this is useful with the Object and Array types since it eliminates the references between instances.

Reactivity in the scope of the webcomponent

Atomico removes the use of "this" given its functional approach, but adds the hook [useProp] (hooks / useprop.md) which allows to reference a prop for use with a functional syntax, eg:

Recommended articles

Syntax

Example

Observation

The reference object is useful for referencing nodes between customHooks.

Cycle as attribute:

Cycle as property:

evaluates if the value is of the declared type:

• If it corresponds to the type:

  1. It is saved in props.

  2. An event is emitted (if this has been configured in the prop).

  3. It is reflected as an attribute (if this has been configured in the prop).

  4. It is sent to the update queue and subsequent rendering.

• It does not correspond to the type: an error is created by console with the following data:

  • target: Instance of the webcomponent.

  • value: Input value.

  • type: expected type.

Syntax

JSX

Atomico supports jsx-runtime, alternatively you can import the h function to declare manual of the JSX pragma, eg:

Template String

Return rule

An important rule of Atomico's virtualDOM is that every webcomponent must return the <host/> tag since it represents the state of the webcomponent's DOM, such as:

1. Enable the use of the shadowDOM by declaring the shadowDom property.

2. Association of events, attributes or properties.

3. Template of the webcomponent.

Template

Event Association

Atomico considers that a property must be associated as an event if it is of the function type and begins with the prefix 'on', eg:

Simple lists

Lists with keys

the key property can receive values of the type of any type that allows generating a reference to the node, eg:

Node references

A technique inherited from React, it allows obtaining the reference of the node to which the Ref object is associated through the ref property, example:

shadowDom property

This property allows you to declare the use of the shadowDom, eg:

Method association

You can declare a method by declaring a function in the host tag without using the prefix on in its name, eg:

If when creating or updating the DOM it does not detect the use of the property, it will be associated as a method of this, thus allowing it to be accessed from the DOM, eg:

We invite you to discover part of the development experience you will get with Atomico:

Create really fast webcomponents

Quick components to write since with Atomico you will require fewer lines of code to declare your webcomponents which will help you to be more productive

Fast in performance, since Atomico sends less code to the client, making your interface load quickly

Create web components with less code

This is thanks to a functional orientation inherited from React hooks plus some internal optimization from Atomic that ease the process of shaking the tree at compile time, achieving in this way sending the client a highly optimized JS that only has what you really use

Create webcomponents with a functional orientation

This is thanks to Atomico's reliance on React hooks syntax plus the ability to completely eliminate the need for this when using webcomponents.

Create friendly webcomponents for React, Vue and other libraries

Atomic offers additional coverage for native behavior for React and Vue, allowing your component to be more embed-friendly, example React:

import { Button } from "@formas/button/react";

function App(){
   return <>
      <h1>React App!</h1>
      <Button onClick={()=>console.log("Click!")}>
         Submit
      </Button>
   </>
}

It is normal that the state of your component depends on the references of a slot, this hook facilitates the process of observing these references without the need to associate the changes to a state.

Syntax

const update = useUpdate();

Where:

1. update: Callback, force component update.

Syntax

const refHost = useHost();

Returns the instance of the webcomponent in reference format, this reference allows to extend behaviors when creating customHooks.

Example

import { useHost, useEffect } from "atomico";

function useListener(type: string, callback: (ev: Event) => void) {
  const ref = useHost();
  useEffect(() => {
    const { current } = ref;
    current.addEventListener(type, callback);
    return () => current.removeEventListener(type, callback);
  }, []);
}

From the example we can highlight that useListener is a customHook that allows listening to an event from the webcomponent without the need to link said event to the VirtualDOM.

useProp allows you to work with a prop(property) of the webcomponent in a similar way to useState.

Syntax

const [value, setValue] = useProp(myProp);

Where :

• value: Current value of the prop.

• setValue: Callback to update the value of the prop.

• myProp: string, defines the name of the prop to be used by the hook.

Example

import { useProp } from "atomico";

function useCounter(prop) {
  const [value, setValue] = useProp(prop);
  return {
    value,
    increment: () => setValue((value) => value + 1),
    decrement: () => setValue((value) => value - 1),
  };
}

function component() {
  const counter = useCounter("value");
  return (
    <host>
      <button onClick={counter.increment}>+</button>
      <strong>{counter.value}</strong>
      <button onClick={counter.decrement}>-</button>
    </host>
  );
}

component.props = {
  value: { type: Number, value: 0 },
};

import { useProp } from "atomico";

function useCounter(prop) {
  //                                 👇 type for prop
  const [value, setValue] = useProp<number>(prop);
  return {
    value,
    increment: () => setValue((value) => value + 1),
    decrement: () => setValue((value) => value - 1),
  };
}

function component() {
  const counter = useCounter("value");
  return (
    <host>
      <button onClick={counter.increment}>+</button>
      <strong>{counter.value}</strong>
      <button onClick={counter.decrement}>-</button>
    </host>
  );
}

component.props = {
  value: { type: Number, value: 0 },
};

Where:

1. useCounter is a customHook and that it can work with any property of the webcomponent of type Number.

2. useCounter returns 2 methods increment and decrement that modify the value of the prop.

3. useCounter can be instantiated multiple times for different properties.

Syntax

const [state, setState] = useState(optionalInitialState);

Where:

1. const [state,setState] : Return of useState, the arguments allow reading and updating of the state associated with the hook instance.

   • state : Current state.

   • setState: Current status updater.

2. useState( optionalInitialState ): Function that associates the state to the webcomponent:

   • optionalInitialState: Optional parameter that defines the initial state associated to the hook instance, If optionalInitialState is a function it will be executed in order to obtain the initial state only at the moment of the hook instance for the first time.

Example

function MyComponent() {
  const [count, setCount] = useState(0);
  return <host onclick={() => setCount(count + 1)}> {count} </host>;
}

Syntax

const dispatchEvent = useEvent(myEvent, eventInit);

Where:

• dispatchEvent: callback, dispatches the event from the webcomponent and allows defining the detail by receiving a first parameter

• myEvent: string, name of the event to dispatch.

• eventInit: optional object, event configuration.

Examples

import { useEvent } from "atomico";

function component() {
  const dispatchEvent = useEvent("clickButton", {
    bubbles: true,
    composed: true,
  });
  return (
    <host>
      <button onclick={() => dispatchEvent()}>button</button>
    </host>
  );
}

import { useEvent } from "atomico";

function component() {
  const dispatchEvent = useEvent("clickButton", {
    bubbles: true,
    composed: true,
  });
  return (
    <host>
      <button onclick={() => {
        const detail = "my-component"; // 👈
        dispatchEvent(detail);         // 👈
      }}>button</button>
    </host>
  )c

import { Host, useEvent } from "atomico";

type DetailClickButton = {id: number};
//                             👇 declaration to associate event to JSX/TSX
function component():Host<{onclickButton: CustomEvent<DetailClickButton>}> {
//                             👇 type for detail
  const dispatchEvent = useEvent<DetailClickButton >("clickButton", {
    bubbles: true,
    composed: true,
  });
  return (
    <host>
      <button onclick={() => {
        //            👇 Detail
        dispatchEvent({id:100});
      }}>button</button>
    </host>
  );
}

Event customization

The second parameter of useEvent allows customizing the behavior of the even:

interface EventInit {
  // Allows the event to be dispatched upstream to the node's containers.
  bubbles?: boolean;
  // Allows the event to traverse the shadowDOM event capture.
  composed?: boolean;
  // Allows the event to be canceled.
  cancelable?: boolean;
  // Allows customizing the event builder, ideal for event instance-based communication.
  base?: Event | CustomEvent;
}

Recommended articles

Hooks only for webcomponents

Hooks homogolates of React

@atomico/hooks

Syntax

Where :

1. effectCallback : Function that is executed one or more times according to optionalArgumentList,effectCallback can return a function that will be executed only if effectCallback is executed again or the webcomponent is unmounted.

2. optionalArgumentList: Array of arguments that controls the execution of effectCallback, if an argument ofoptionalArgumentList changes it will trigger that effectCallback is executed again without first cleaning the effects subscribed by the previous execution.

Example

useLayoutEffect

useLayoutEffect replicates the logic of useEffect but with synchronous execution after rendering.

useInsertionEffect

useLayoutEffect replicates the logic of useEffect but with synchronous execution before rendering.

Syntax

Where :

1. memoValue : Return memorized by useMemo.

2. callback: Function that is executed one or more times according to optionalArgumentList.

3. optionalArgumentList: Array of arguments that controls the execution of callback, if an argument of optionalArgumentList changes it will trigger that callback is executed again.

useCallback

Hook that allows you to memorize a callback so that it keeps its scope

Where:

1. memoCallback : Return memorized by useCallback.

The purpose of this hook is to facilitate the consumption of promises.

Syntax

import { usePromise } from "atomico";

const callback = (id: number) => Promise.resolve(id);
const args: Parameters<typeof callback> = [1];
const autorun = true;

const promise = usePromise( callback, args, autorun );

where:

• callback : asynchronous function.

• args: arguments that callback requires.

• autorun: by default true, it automatically executes the promise, if it is false the execution of the promise is suspended.

• promise : return object, at the type level it defines the following properties:

  • pending: boolean, defines if the promise is executed but pending resolution.

  • fulfilled: boolean, defines if the promise has been fulfilled

  • result: result of the promise.

  • rejected: boolean, defines if the promise has been rejected.

Example

import { usePromise } from "atomico";

const getUsers = (id: number) => Promise.resolve({ id, name: "Atomico" });

function component() {
  const promise = usePromise(getUsers, [1]);

  return (
    <host>
      {promise.fulfilled ? (
        <h1>Done {promise.result.name}!</h1>
      ) : promise.pending ? (
        <h1>Loading...</h1>
      ) : (
        <h1>Error!</h1>
      )}
    </host>
  );
}

useId is a Atomico Hook for generating unique IDs that can be passed to accessibility attributes.

Syntax

Example

Use ID generate a unique ID for each component, this id can be useful for referencing CSS selectors or creating names for inputs that only the component knows about.

With the new contexts API you will be able to easily communicate components without the need to handle events, by default the communication is top down, but through it you can share anything as long as it is defined as an object.

Atomico's api is similar to React's Context api, let's explore the behavior of Atomico's context api:

createContext

create a custom Element as a context, this will serve to synchronize all the components nested within it, you must always remember to declare the tagname of this customElement, example

useContext

It allows to consume the return of createContext, let's go back to the previous example and suppose that we want to consume the customElement Theme created by createContext, the code for this would be the following:

In this way useContext captures the value of the parent component or reuses the value given by default to createContext.

Custom context values

By setting the value prop on the context, you can pass custom values down the sub-tree:

When to use the Context API?

It is ideal to always prioritize a conversation between parent and child through events or props api, but sometimes the depth of the DOM makes this process difficult, for this the context api has been introduced. To remove DOM depth limitations and ensure synchronization based on a unique identifier, some ideal cases to solve with the context api are:

1. Synchronize states or private methods between components.

2. Share a value or states inherited from the parent regardless of DOM depth.

useAsync

with a similar approach to React's use hook, but with scope approach.

scope approach? yes, this hook seeks to resolve a promise from a callback return, this allows you to regenerate the promise according to the scope, example:

import { useAsync } from "atomico";

const getUser = (userId) => fetch(`users/${userId}`).then((res) => res.json());

function component({ userId }) {
  const user = useAsync(getUser, [userId]);
  return (
    <host>
      <h1>name: {user.name}</h1>
    </host>
  );
}

component.props = { userId: Number }

import { Props, useAsync } from "atomico";

const getUser = (userId: number): Promise<{ name: string }> =>
  fetch(`users/${userId}`).then((res) => res.json());

function component({ userId }: Props<typeof component>) {
  const user = useAsync(getUser, [userId]);
  return (
    <host>
      <h1>name: {user.name}</h1>
    </host>
  );
}

component.props = { userId: Number };

where:

• getUser: async callback.

• [ userId ]: arguments that if changed regenerate the promise.

• user : promise return

Like useEffect, the promise will be executed every time the arguments to the second parameter of useAsync change.

useSuspense

allows to listen to all useAsync executions nested in the component, example:

function component() {
  const status = useSuspense();
  return (
    <host shadowDom>
      {status.pending ? "Loading..." : status.fulfilled ? "Done!" : "Error!"}~
      <slot />
    </host>
  );
}

This hook enables you to take control of the context from the component that instantiates useProvider, thus avoiding the need to instantiate the context node in the DOM.

Example of the useProvider hook:

import { createContext, useProvider, c } from "atomico";

export const Theme = createContext({
    color: "white",
    background: "black"
});

export const App = c(()=>{
    useProvider(Theme,{
        color: "red",
        background: "yellow"
    });
    
    return <host shadowDom><slot/></host>
});

Objective

Avoid creating an instantiable context node in the DOM.

The idea is to create an instance of AbortController every time the hook's parameters change. Each parameter change will abort the previously generated controller, thus cancelling any subscribed promises.

Example

import { useAsync, useAbortController } from 'atomico';

async function getUser(id: number, signal: AbortSignal) {
  return fetch(`/id/${id}`, { signal });
}

function myComponent({ userId }: Props<typeof myComponent>) {
  const { signal } = useAbortController([userId]);

  const user = useAsync(getUser, [userId, signal]);

  return <host>{user.name}</host>;
}

myComponent.props = { userId: { type: Number, value: 0 } };

The significant advantage of using useAbortController is the automatic cancellation of asynchronous processes that depend on it when modifying the arguments provided to useAbortController (similar to useEffect).

The "atomico/test-hooks" submodule is a direct part of Atomico's core and will allow you to run the customHook in a controlled way without the need for webcomponents.

import { createHooks } from "atomico/test-hooks";

createHooks

function that creates an isolated context that is shared globally with Atomico hooks when executing the load method

Instance

const hooks = createHooks(opcionalRender, opcionalHost);

Where:

• optionalRender: Callback that allows restarting the hook's life cycle, this callback will be executed every time a hook like useState or useReducer requests the scope update, Atomico uses it to render the webcomponent again.

• opcionalHost: allows to share an object for the hook useHost, Atomico uses it to share the instance of the webcomponent.

Return of the instance

interface Hooks {
  load<T>(callback: () => T): T;
  clearEffect(unmounted?: boolean): () => ()=> void;
}

Where:

• load: Function that allows to load the hooks to the temporary global context of Atomico.

• clearEffect: Function that activates the collector of useLayoutEffect, when executing clear Effect a callback will be returned that allows ending the collector for useEffect, closing the cycle of secondary effects.

  If clear Effect receives true as parameter, it communicates the unmounted.

Example:

./use-counter.js: customHook to test.

import { useState } from "atomico";

export function useCounter(initialValue) {
  const [value, setValue] = useState<number>(initialValue);
  return {
    value,
    increment: () => setValue((value) => value + 1),
    decrement: () => setValue((value) => value - 1),
  };
}

./use-counter.test.js: The example is based on the test environment from @web/test-runner.

import { expect } from "@esm-bundle/chai";
import { createHooks } from "atomico/test-hooks";
import { useCounter } from "./use-counter.js";

it("Check return", () => {
  const hooks = createHooks();

  const counter = hooks.load(() => useCounter(10));

  expect(counter.value).to.equal(10);
  expect(counter.increment).to.be.an.instanceOf(Function);
  expect(counter.decrement).to.be.an.instanceOf(Function);
});

Atomico's render cycle works like this:

First, when the component is instantiated, 3 promises will be created pending resolution:

1. componentInstance.mounted: resolved once the connectedCallback has been executed by the customElement.

2. componentInstance.updated: the render cycle for first mount or update is encapsulated in componentInstance.updated.

3. componentInstance.unmounted: resolved once the disconnectedCallback has been executed by the customElement.

Render or rerender cases are:

1. First render.

2. Updating a property or attribute.

3. Update dispatched by a hook

Remember all updates are stacked into a single big loop of componentInstance.updated.

This improves the testing experience since to observe the changes you only have to wait for the resolution of componentInstance.updated , example:

import { html } from "atomico";
import { expect } from "@esm-bundle/chai";
import { fixture } from "atomico/test-dom";
import { Component } from "./component.js";

describe("my test", () => {
  it("my-component", async () => {
    const componentInstance = fixture(html`<${Component}>
        <span>content...</span>
    </${Component}>`);

    await componentInstance.updated; // fist render

    componentInstance.myProp1 = 10;
    componentInstance.myProp2 = 20;
    componentInstance.myProp3 = 20;

    await componentInstance.updated; // now we can observe the effects on the DOM from the previous updates
    
    await componentInstance.unmounted; // the component has been unmounted
  });
});

Webcomponent as function

The first rendering as the update of a prop will call to execute again the function that defines our component, Atomico internally stores the references to support the Hooks api and will render the virtualDOM returned by said function, this is encapsulated within componentInstance.updated

function component(){
    useEffect(()=>{
        console.log("Component mounted");
        ()=> console.log("Component unmounted");
    }, []);
    return <host/>
}

SSR

Atomico allows modifying its life cycle in cases of SSR, improving the rendering of the CSS in case of SSR and avoiding the effects of useEffect and useLayoutEffect

import {options} from "atomico";

// replace the internal use of CSS StyleSheet by the style tag
options.sheet = false; 

// will avoid hook side effects
options.ssr = true; 

Hydration

Technique to reuse the DOM generated by the SSR, Atomico only in the first render of the component that declares date-hydrate will retrieve the existing DOM in the DOM not created by Atomico to relate it to the virtualDOM, avoiding creating the node again.

Optimization

Atomico by default has a good performance, but it can be further optimized if certain techniques are applied.

Render optimization with static nodes

const staticDom = (
  <host shadowDom>
    <slot />
  </host>
);
function component() {
  return staticDom;
}

function component() {
  return html`<host shadowDom>
    <slot />
  </host>`;
}

A static node is equivalent to using node.cloneNode(true)

render optimization with renderOnce

function component() {
  return <host shadowDom renderOnce>
    <slot />
  </host>
}

The renderOnce property renders the node only once, one of the advantages of this technique is that the virtualDOM can access the scope of the function.

fixture

function that allows to keep the render on a single node for each execution of it, the container will be unmounted at the end of each execution of it.

import { html } from "atomico";
import { expect } from "@esm-bundle/chai";
import { fixture } from "atomico/test-dom";
import { Component } from "./component.js";

describe("my test", () => {
  it("my-component", async () => {
    const component = fixture(html`<${Component}>
        <span>content...</span>
    </${Component}>`);

    await component.updated;

    /** Test logic */
  });
});

This allows each fixture execution inside it to be related to the container used for the test, allowing you to fily test external DOM changes, example:

import { html } from "atomico";
import { expect } from "@esm-bundle/chai";
import { fixture } from "atomico/test-dom";
import { Component } from "./component.js";


describe("my test", () => {
  it("my-component", async () => {
    // first instance of the render, it will return the component
    const component = fixture(html`<${Component}>
        <span>content...</span>
    </${Component}>`);

    await component.updated;
    
    // updates the content of the span tag of the first instance of the render
    fixture(html`<${Component}>
        <span>new content...</span>
    </${Component}>`);
    
    await component.updated;

    expect(
          component.querySelector("span").textContent
    ).to.equal("new content...");
  });
});

We recommend the @web/test-runner tool, if your project was created with the command npm init @atomico the test environment will be preconfigured, you can see this pre-configuration at https://github.com/atomicojs/base/tree/2-started.

Advanced (Documentation in progress)

To scale the test environment you can complement with tools such as:

1. Cypress: allows you to automate interactions and evaluate interactions of your interface.

2. Percy: Allows you to evaluate the appearance changes of your component or application between versions.

1. Its name cannot have the on prefix since, if it does, Atomico will recognize it as a property expecting to listen to the event.

2. It can only have one listener, limiting others from observing the event.

We recommend:

1. Using the useEvent hook to dispatch component-level events or any custom hook.

2. Using the Prop.event API to dispatch events when the observed prop changes.

Always prefer the two previously mentioned methods, as they allow you to:

1. Define if the event bubbles.

2. Define if the event is cancelable.

3. Define if the bubbling event can penetrate the shadow DOM.

4. Define a custom constructor for the event.

5. Having multiple listeners for the event

When is it recommended to use a callback as a prop?

Cuando se busca comunicar parametros o leer el retorno de este, ejemplo:

const MyForm = c(
  ({ getPosts }) => {
    const posts = useAsync(getPosts, []);

    return <host></host>;
  },
  {
    props: {
      getPosts: {
        type: Function,
        value: async (): Promise<{ id: number; title: string }[]> => [],
      },
    },
  }
);

If you are a React user, it is common for you to make component declarations like these:

export function MyComponent(){
    return <>My component in react</>
}

Thanks to the previous code in React we can:

1. Instantiate your component through its function, example <MyComponent>

2. Friendly export component as module

In Atomico there are some small differences 👇

we recommend in Atomico

Export the return of the c function, since it is instantiable at the JSX level or when using the new operator, example:

function myComponent(){
    return <host>My component in Atomico</host>
}

export const MyComponent = c(myComponent);

customElements.define("my-component", MyComponent);

import { MyComponent } from "./my-component";

function app(){
    return <host>    
        <MyComponent/>
    </host>
}

import { MyComponent } from "./my-component";

const component = new MyComponen; 

import "./my-component";

const component = document.createElement("my-component");

<my-component></my-component>

Gracias a lo anterior podemos:

1. Instantiate your component with TS-level type validation either by using JSX or the new operator with, but remember that to get this type of instances you must first have registered your customElement in the same file or another.

2. Export the useful component to instantiate.

Yes, but Atomico doesn't only depend on ESM, it also depends on the following api's that you will have to cover with Polyfill or some bundle tool.

1. ESM modules: documentation - caniuse

2. CustomElements: documentation - caniuse

3. ShadowRoot: documentation - caniuse

4. Map: documentation - caniuse

5. Symbol and Symbol.for: documentation - caniuse

6. append and prepend: documentation - caniuse

7. Declarative Shadow DOM: Only for using SSR with webcomponents that use shadowDOM. documentation

Let's understand that today Atomico covers 94% of existing browsers without the need for polyfills or packers, the 6% not covered are usually browsers like ie11 or others.

If you depend on the uncovered segment of browsers you can use the following tools to support the apis necessary for Atomico to work.

polyfill-fastly.io to associate Map, Symbol, append and prepend.

https://github.com/Rich-Harris/shimport to associate esm.

https://github.com/ungap/custom-elements to associate customElements apis.

Atomico makes it easy to declare events at the type level using the Host type.

Example

import { Host, c, useEvent } from "atomico";

type CustomDetail = { timestamp: number };

const MyComponent = c(
  (): Host<{ onMyCustomEvent: CustomEvent<CustomDetail> }> => {
    const dispatch = useEvent<CustomDetail>("MyCustomEvent");
    return (
      <host>
        <button
          onclick={() => {
            dispatch({ timestamp: Date.now() });
          }}
        >Click</button>
      </host>
    );
  }
);

In the previous code, we have declared the onMyCustomEvent event at the type level. According to the template logic, this event will be dispatched every time the button is clicked, and the detail attached to this event will be of type CustomDetail.

import { Component } from "atomico";

// 📌 Parameters for the function and set 
//    the structure rules for myComponent.props
interface Props{
    checked: boolean;
    value: string
}

// 📌 Optional, improves the typing experience 
//    in JSX (Atomico, Preact and React)
interface MetaProps {
    myMethod:(value: number)=>void;
    onMyEvent: Event;
}

const myComponent: Component<Props, MetaProps> = (props) => {
    const myMethod = (value: number)=>{};
    return <host myMethod={myMethod }></host>
}

myComponent.props = {
    checked: Boolean,
    value: { type: String, event: {type: "MyEvent"} },
}

The declaration const myComponent: Component<Props, MetaProps> defines at the Typescript level the types of props and other options with which the component should be structured.

This process is strict but makes autocompletion and error detection easier in the component declaration.

Some warnings that this type can create are:

1. The declaration of the prop in myComponents.props does not match the type declared in Props.

2. A props declaration is missing.

3. Props has invalid metadata, example reflect has been defined for a Promise type.

With Atomico and Typescript you will be able to:

📌 If you are a Typescript user I recommend using TSX vs the template-string, as you will benefit from:

1. JSX runtime, Typescript will automatically import Atomico upon detecting the use of TSX.

2. Autocompletion and validation of attributes, properties and events of tags and webcomponents.

3. Webcomponent instance validation using constructors.

Construct the props parameter of your functional component.

Your component as a function does not infer the props, to help infer the props you should use the Props type, example:

From an object: Construct props directly from the declaring object.

From the component: Build the props from the component, internally Atomico captures the property component.props.

From another customElement component: It's unusal, but when you extend another component you can infer the props from its constructor.

Check the correct declaration of your component.

Typescript checks the structure of your component by using the c function on it, thus validating which props and styles have been attached.

The return of c is a CustomElement with the types of the associated props, example:

It will report an error to Typescript since this component's props define that value is of type number, this validation also applies when instantiating your CustromElement in JSX or TSX.

Both TSX or JSX will help you to build better applications since it verifies the types according to the definition of its component, this verification is Free, it does not need plugins, only a tsconfig.json file and Typescript to automate the revision.

The Props type allows you to infer the types of props already declared in the props object, example:

import { Props } from "atomico";

function myComponent(props: Props<typeof myComponent>) { // {checked: boolean}
    return <host>Hello {props.checked?"Yes":"No"}</host>
}

myComponent.props = {
    checked: Boolean,
}

The main difference with the Component type is that Props does not generate stricture rules for the component, it only infers the props object to be used as an argument.

At the Typescript Props level, it does evaluate the structure of the component, in order to correctly infer the props, so if the component has a writing error, a warning about this type will be displayed.

When to use the shadow Dom?

By creating a UI solution that coexists in the web ecosystem such as HTML, libraries and frameworks, since the shadowDOM allows you to:

1. Protect your UI from libraries like React, Vue and others

2. Associate styles natively, efficiently and safely

3. Reference lightDOM content in the shadowDOM

Webcomponents with Shadow DOM are ideal for creating cross UI solutions as they coexist without conflict with the entire web ecosystem.

Why use shadowDOM?

To protect our component at the DOM manipulation level and take advantage of some of the benefits of the shadowDOM such as:

1. Slot management

2. CSS appearance of web component.

3. The shadowDOM is ideal for creating components that interact with libraries like React, Vue or others. The ShadowDOM protects the DOM it contains from manipulations generated by other libraries.

Slot management

Slots allow us to reflect existing nodes in the lightDOM into the shadowDOM, example:

This is really useful, since we can group slots according to their name in a specific place of the webcomponent.

We invite you to learn more about slots through the following guide:

CSS appearance of web component.

The shadowDOM allows you to do something fantastic, protect your CSS from global styles, this has 2 great advantages:

1. The appearance of our component will not be affected by global CSS declarations.

2. Customization protected by CSS custom Properties

We invite you to learn more about handling styles in atomic through the following guide:

Meta-types allow you to define properties not covered by Atomico's Automatic support, such as:

React and webcomponents

React has begun to support the use of webcomponents in an experimental way, this will allow to use custom tag with association of events and more, example:

import React from "react";
import "@formilk/components";

export default function App() {
  return (
    <fm-button>Click!<fm-button>
  );
}

Advantages: The react team will take care of the coverage of this characteristic.

Disadvantages: (Optional) The maintainer of the component must declare the types of the custom tag.

Although the use of the custom tag is a way of instantiating the component, many times it does not define the import path at the time of its use, complicating the resolution of the component's origin, to avoid this we recommend the use of the Atomico wrapper for React.

Atomico wrapper for React

Atomico the package @atomic/react allows:

1. Create a Wrapper component for the custom Element

2. Avoid react conflicts with webcomponents, such as association of events, attributes, properties and children.

3. Reflect the types declared in Atomic to React, valid for JSX or TSX

Coverage is automatic if you decide to share your package using @atomico/exports under the following export conditions.

Atomico inside Next.js

All webcomponents work in Next if it escapes from SSR

Example of custom tag usage

import  "@formilk/components/button";

export default function Home() {
  return (
    <div>
      <fm-button name="Matias">
        <h1>Hello Next.js</h1>
      </fm-button>
    </div>
  );
}

Example of use of the wrapper.

import dynamic from "next/dynamic";

const Button = dynamic(() => import("./wrapper-button.js"), {
  ssr: false,
});

export default function Home() {
  return (
    <div>
      <Button  name="Matias">
        <h1>Hello Next.js</h1>
      </Button>
    </div>
  );
}

import { auto } from "@atomico/react/auto";
import { Button } from "@formilk/components/button";

export default auto(Button);

Remember if you use the auto module, it should always be imported first than the customElement to use, otherwise auto will generate an id as a custom tag to instantiate the component within react

Host to declare events

Host will be useful for you to declare your event using JSX or TSX regardless of its origin, example:

The use of Host allows that when using JSX or TSX your event is validated through Typescript, this also applies when using @atomico/react, example:

Note event.currentTarget accesses the CustomElement, example properties and more.

That has another benefit, capturing the event as a type to be used in an external handler, example:

Atomico allows the definition of methods from the host tag, this in order to share the scope with the methods (Functions) of the component, but this escapes the definition of types, to patch this we must use the Host type, this will allow us to validate the method from the JSX, TSX and the component instance.

Host to method declaration

@atomico/exports

CLI that decorates the package.json according to the code to be exported in order to share your code optimally. By using the --wrappers flag the CLI will detect the export of webcomponents and automatically create a wrapper for React, Preact and Vue.

@atomico/react

With this package you will be able to create wrappers for your Webcomponents in React, even managing to make SSR of your webcomponents in environments like Next.js with these wrappers.

useState

useState infers the type according to its initial state, if you don't define that state you can define the type manually, example:

The above statement will define that:

1. message is of type string.

2. setMessage only accepts values of type string or functions that return a string.

useProp

useProp will not infer the type from the prop, you must define it, example:

Let's remember that useProp has a return api similar to useState, so the previous declaration will define that:

1. message is of type string.

2. setMessage only accepts values of type string or functions that return a string.

useMemo and useCallback

both useMemo vs useCallback infer its type based on the callback that builds the memo state, but for certain conditions you may need to force the type return, example:

Although useMemo infers that its type is string, you can change the return rules via the first type parameter.

The above statement will define that:

1. message is of type string.

This applies equally to useCallback.

useEvent

useEvent allows defining the detail structure through the type parameter, example:

The above statement will define that:

1. The dispatch callback expects an object of type {id: string} as a parameter.

useRef

useRef allows to define through the type parameter the expected value of current in the reference.

The above statement defines:

1. refForm?.current is of the type HTMLFormElement.

useHost

useHost defines that current always exists, so the optional selector is not necessary, the type parameter of useHost allows to define the source Element, example:

All hooks in Atomico have Type declarations, explore them when importing each hook as a documentation source.

Although the props today offer strict rules, Type allows them to be complemented with a direct definition of the types to accept, example:

import { Props } from "atomico";

function component(){
    return <host/>
}

component.props = {
    value: String as Type<"A"|"B"|"C">
}

The above is equivalent to using value as a function, example:

import { Props } from "atomico";

function component(){
    return <host/>
}

component.props = {
    value: {
        type: String,
        value: ():"A"|"B"|"C"=>"A"
    }
}

This is also valid for the null type that in Atomic translates as Any, example:

component.props = {
    src: null as Type<string | Promise<any>>
}

Atomico escapes React DOM immutability logic and moves closer to the native DOM API, this means that Atomico at the scope level is only responsible for receiving the props and rendering the DOM, but it does not observe the internal mutations of the DOM automatically, this is because the native level mutations can come from anywhere, for example other libraries. Now for ensure state synchronization it is convenient that every webcomponent that wants to be observed has the obligation to dispatch a change event

You can easily achieve this by using useEvent or Prop.event, applying that you can:

capture change as event

const [ value, setValue ] = useState("init"); // you can also use useProp

<host>
    <my-component 
        value={value} 
        onchange={({target})=>setValue(target.value)}
    ></my-component>
</host>

Force a fixed value

const update = useUpdate();

<host>
    <my-component 
        value={value} 
        onchange={update}></my-component>
</host>

the update function forces an update on the component, in order to redefine value according to the scope

Atomico has 3 great hooks to solve asynchronous tasks:

1. usePromise: Processes asynchronous tasks and shows the status and resolution of these

2. useAsync: Allows you to pause rendering until a promise is resolved

3. useSuspense: Allows to know the paused states product of the use of useAsync nested in the component