Question

所以，我正在阅读ReactJS Getting Started guide。我遇到了我修改过的this component (JSFiddle)。

如您所见，当您更改SearchBar组件时，它会更改父FilterableProductTable的状态。然后调用父#render方法，重新创建SearchBar，并再次调用SearchBar＃render方法。

/** @jsx React.DOM */

var ProductCategoryRow = React.createClass({
    render: function() {
        return (<tr><th colSpan="2">{this.props.category}</th></tr>);
    }
});

var ProductRow = React.createClass({
    render: function() {
        var name = this.props.product.stocked ?
            this.props.product.name :
            <span style={{color: 'red'}}>
                {this.props.product.name}
            </span>;
        return (
            <tr>
                <td>{name}</td>
                <td>{this.props.product.price}</td>
            </tr>
        );
    }
});

var ProductTable = React.createClass({
    render: function() {
        console.log(this.props);
        var rows = [];
        var lastCategory = null;
        this.props.products.forEach(function(product) {
            if (product.name.indexOf(this.props.filterText) === -1 || (!product.stocked && this.props.inStockOnly)) {
                return;
            }
            if (product.category !== lastCategory) {
                rows.push(<ProductCategoryRow category={product.category} key={product.category} />);
            }
            rows.push(<ProductRow product={product} key={product.name} />);
            lastCategory = product.category;
        }.bind(this));
        return (
            <table>
                <thead>
                    <tr>
                        <th>Name</th>
                        <th>Price</th>
                    </tr>
                </thead>
                <tbody>{rows}</tbody>
            </table>
        );
    }
});

var SearchBar = React.createClass({
    handleChange: function() {
        this.props.onUserInput(
            this.refs.filterTextInput.getDOMNode().value,
            this.refs.inStockOnlyInput.getDOMNode().checked
        );
    },
    render: function() {
        console.log('This SearchBar#render is being called every time the state changes!');
        return (
            <form>
                <input
                    type="text"
                    placeholder="Search..."
                    value={this.props.filterText}
                    ref="filterTextInput"
                    onChange={this.handleChange}
                /><span data-something={this.props.filterText}>Edit this text manually with the DOM inspector. Type something on the text box. Look that the data-something property is re-rendered, but this text is kept the same</span>
                <p>
                    <input
                        type="checkbox"
                        value={this.props.inStockOnly}
                        ref="inStockOnlyInput"
                        onChange={this.handleChange}
                    />
                    Only show products in stock
                </p>
            </form>
        );
    }
});

var FilterableProductTable = React.createClass({
    getInitialState: function() {
        return {
            filterText: '',
            inStockOnly: false
        };
    },

    handleUserInput: function(filterText, inStockOnly) {
        this.setState({
            filterText: filterText,
            inStockOnly: inStockOnly
        });
    },

    render: function() {
        return (
            <div>
                <SearchBar
                    filterText={this.state.filterText}
                    inStockOnly={this.state.inStockOnly}
                    onUserInput={this.handleUserInput}
                />
                <ProductTable
                    products={this.props.products}
                    filterText={this.state.filterText}
                    inStockOnly={this.state.inStockOnly}
                />
            </div>
        );
    }
});


var PRODUCTS = [
  {category: 'Sporting Goods', price: '$49.99', stocked: true, name: 'Football'},
  {category: 'Sporting Goods', price: '$9.99', stocked: true, name: 'Baseball'},
  {category: 'Sporting Goods', price: '$29.99', stocked: false, name: 'Basketball'},
  {category: 'Electronics', price: '$99.99', stocked: true, name: 'iPod Touch'},
  {category: 'Electronics', price: '$399.99', stocked: false, name: 'iPhone 5'},
  {category: 'Electronics', price: '$199.99', stocked: true, name: 'Nexus 7'}
];

React.renderComponent(<FilterableProductTable products={PRODUCTS} />, document.body);

然而。如果我通过浏览器检查器手动编辑SearchBar组件的DOM，当我在文本框中键入内容时，SearchBar会被呈现（您可以看到DOM上的数据属性更改），但手动修改的DOM不会＃ 39;改变，这意味着实际上并不是渲染所有东西，只是改变的东西。

那么，它是如何做到的呢？在幕后进行脏检查吗？ HTML上的差异？

Answer 1

我找到了答案。 ReactJS使用Diff algorithm with the virtual DOM，它显然足够快速和智能。它还允许您在组件上设置shouldComponentUpdate方法，告诉它在某些情况下不应该重新渲染。

ReactJS如何知道究竟要重新渲染的内容？

1 个答案: