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setStateを複数回実行してもrenderは1回しか呼ばれない

Last updated at Posted at 2015-03-29

ReactjsのsetStateとrenderの挙動をちょっと確認してみました。
具体的には以下のコードで検証。

はじめはsetStateの度にrenderが呼び出されるのかと思ってましたが
そうではなくて、stateの変更をキューに入れてrenderを呼び出す前にまとめて解決するようです。
setTimeoutでコールバックを呼んだ時なんかは
別のキューになるようです
setStateが呼ばれなければもちろんrenderも呼ばれない

app.js

var MyComponent = React.createClass({
	getInitialState: function () {
    return {
    	value: 'step 0'
    };
	},
	handleClick: function() {
		this.setState({
			value: 'step 1'
		});
		console.log('called step 1');

		this.setState({
			value: 'step 2'
		});
		console.log('called step 2');

		this._func();
		this.setState({
			value: 'step 4'
		});
		console.log('called step 4');
		setTimeout(this._callback, 1000, this);
	},
	_func: function() {
		this.setState({
			value: 'step 3 this is inner func'
		});
		console.log('step 3 _func called');
	},
	_callback: function(self) {
		self.setState({
			value: 'step 5'
		});
		console.log('step 5 called');
	},
	doNothing: function() {
		console.log('do nothing');
	},
	render: function() {
		console.log('will render!');
		return (
			<div>
				<div>{this.state.value}</div>
				<a onClick={ this.handleClick }>Click me!</a>
				<p onClick={ this.doNothing }>Click me but I will do nothing</p>
			</div>
		);
	}
});
React.render(
	<MyComponent />,
	document.getElementById('app')
);

//will render! 最初
//app.js:44 called step 1
//app.js:49 called step 2
//app.js:62 step 3 _func called
//app.js:55 called step 4
//app.js:74 will render! 一回だけ呼ばれる
// 1秒空くよ
//app.js:74 will render!  順番が違う?
//app.js:68 step 5 called
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