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atomico-hooks-core

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Use core Atomico hooks: useState, useMemo, useCallback, useRef, useHost, useUpdate, useId, useHook. Triggers when the user needs local state management, memoization, DOM references, or access to the host element in Atomico components. Do NOT trigger for React hooks — Atomico hooks have the same API but run in a web component context with different lifecycle semantics.

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Core Hooks

useState — Local Reactive State

Works identically to React's useState. Accepts an initial value or a factory function. Returns [value, setter].

import { c, useState } from "atomico";

const Counter = c(() => {
    const [count, setCount] = useState(0);

    return (
        <host>
            <span>{count}</span>
            <button onclick={() => setCount(count + 1)}>+</button>
            <button onclick={() => setCount((prev) => prev - 1)}>-</button>
        </host>
    );
});

Type Inference

// Inferred as number
const [count, setCount] = useState(0);

// Explicit generic for undefined initial state
const [active, setActive] = useState<boolean>();

// Factory function — type inferred from return
const [items, setItems] = useState<string>(() => "welcome");

// Complex types
const [values, setValues] = useState<[number, number, number, number]>([1, 2, 3, 4]);

Setter Behavior

The setter only triggers an update if the new value is strictly different (!==) from the current value.

setCount(5);                       // Direct value
setCount((prev) => prev + 1);     // Functional update

useMemo — Memoized Computation

Caches the return of a callback. Only recomputes when dependencies change.

import { useMemo } from "atomico";

const expensive = useMemo(() => computeHeavyValue(data), [data]);

Type Inference

// Type inferred from callback return
const result = useMemo(() => 42, []);  // number

const isValid = useMemo(() => {
    return dateToValidate.getFullYear() === 2022;
}, [dateToValidate]);  // boolean

useCallback — Memoized Function Reference

Shorthand for useMemo(() => callback, args). Returns the same function reference until dependencies change.

import { useCallback } from "atomico";

const handler = useCallback(
    (param: boolean) => param ? 10 : 0,
    [dependency]
);

useRef — Persistent Mutable Reference

Creates a persistent reference object { current } that survives re-renders. Commonly used for DOM element references.

import { c, useRef } from "atomico";

const MyComponent = c(() => {
    const inputRef = useRef<HTMLInputElement>();

    return (
        <host shadowDom>
            <input ref={inputRef} />
            <button onclick={() => inputRef.current?.focus()}>
                Focus
            </button>
        </host>
    );
});

Typed Refs for Atomico Components

import { useRef } from "atomico";
import { MyChild } from "./my-child.js";

// Use typeof to get the constructor type
const childRef = useRef<typeof MyChild>();

childRef.current?.myProp;  // Full type inference on component props

useHost — Access the Host Element

Returns a ref to the host custom element. Essential for accessing the DOM node, dispatching events, or manipulating the element itself.

import { c, useHost } from "atomico";

const MyComponent = c(() => {
    const host = useHost();

    // Access the host element
    host.current.updated.then(() => {
        console.log("Component rendered!");
    });

    return <host><p>Hello</p></host>;
});

Note: useHost() returns { current: HTMLElement } — the current property always points to the web component instance.

useUpdate — Force Re-render

Returns the component's update function. Calling it triggers a re-render without changing any state.

import { c, useUpdate } from "atomico";

const MyComponent = c(() => {
    const update = useUpdate();

    return (
        <host>
            <button onclick={() => update()}>Force re-render</button>
        </host>
    );
});

useId — Stable Unique Identifier

Generates a unique, stable ID for the current hook position. Useful for accessibility attributes.

import { c, useId } from "atomico";

const MyComponent = c(() => {
    const id = useId();

    return (
        <host shadowDom>
            <label for={id}>Name</label>
            <input id={id} />
        </host>
    );
});

useHook — Low-Level Custom Hook Primitive

The foundational hook for building custom hooks. Manages persistent state across renders using a callback pattern.

import { useHook } from "atomico";

const useMyCustomHook = () => {
    return useHook((state = { count: 0 }) => {
        state.count++;
        return state;
    });
};

Advanced: useHook is the building block for useState, useMemo, and all other hooks. Use it when none of the built-in hooks fit your needs.