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API Reference



Preact.Component

Component is a base class that you will usually subclass to create stateful Preact components.

Component.render(props, state)

The render() function is required for all components. It can inspect the props and state of the component, and should return a Preact element or null.

import { Component } from 'preact';

class MyComponent extends Component {
    render(props, state) {
        // props === this.props
        // state === this.state

        return <h1>Hello, {props.name}!</h1>;
    }
}
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Lifecycle methods

Tip: If you've used HTML5 Custom Elements, this is similar to the attachedCallback and detachedCallback lifecycle methods.

Preact invokes the following lifecycle methods if they are defined for a Component:

Lifecycle methodWhen it gets called
componentWillMountbefore the component gets mounted to the DOM
componentDidMountafter the component gets mounted to the DOM
componentWillUnmountprior to removal from the DOM
componentWillReceivePropsbefore new props get accepted
shouldComponentUpdatebefore render(). Return false to skip render
componentWillUpdatebefore render()
componentDidUpdateafter render()

All of the lifecycle methods and their parameters are shown in the following example component:

import { Component } from 'preact';

class MyComponent extends Component {
    shouldComponentUpdate(nextProps, nextState) {}
    componentWillReceiveProps(nextProps, nextState) {
        this.props // Previous props
        this.state // Previous state
    }
    componentWillMount() {}
    componentWillUpdate(nextProps, nextState) {
        this.props // Previous props
        this.state // Previous state
    }
    componentDidMount() {}
    componentDidUpdate(prevProps, prevState) {}
    componentWillUnmount() {
        this.props // Current props
        this.state // Current state
    }
}
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Preact.render()

render(component, containerNode, [replaceNode])

Render a Preact component into the containerNode DOM node. Returns a reference to the rendered DOM node.

If the optional replaceNode DOM node is provided and is a child of containerNode, Preact will update or replace that element using its diffing algorithm. Otherwise, Preact will append the rendered element to containerNode.

import { render } from 'preact';

// These examples show how render() behaves in a page with the following markup:
// <div id="container">
//   <h1>My App</h1>
// </div>

const container = document.getElementById('container');

render(MyComponent, container);
// Append MyComponent to container
//
// <div id="container">
//   <h1>My App</h1>
//   <MyComponent />
// </div>

const existingNode = container.querySelector('h1');

render(MyComponent, container, existingNode);
// Diff MyComponent against <h1>My App</h1>
//
// <div id="container">
//   <MyComponent />
// </div>
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Preact.h() / Preact.createElement()

h(nodeName, attributes, [...children])

Returns a Preact Virtual DOM element with the given attributes.

All remaining arguments are collected into a children Array, and be any of the following:

  • Scalar values (string, number, boolean, null, undefined, etc)
  • More Virtual DOM elements
  • Infinitely nested Arrays of the above
import { h } from 'preact';

h('div', { id: 'foo' }, 'Hello!');
// <div id="foo">Hello!</div>

h('div', { id: 'foo' }, 'Hello', null, ['Preact!']);
// <div id="foo">Hello Preact!</div>

h(
    'div',
    { id: 'foo' },
    h('span', null, 'Hello!')
);
// <div id="foo"><span>Hello!</span></div>
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