React-router 4
介绍了在router4以后，如何去实现按需加载Component，在router4以前，我们是使用getComponent的的方式来实现按需加载的，router4中，getComponent方法已经被移除，下面就介绍一下react-router4是入围和来实现按需加载的。
1.router3的按需加载方式
route3中实现按需加载只需要按照下面代码的方式实现就可以了。
const about = (location,cb) => {
require.ensure([],require => {
cb(null,require('../Component/about').default)
},'about')
}
//配置route
<Route path="helpCenter" getComponent={about} />
2.router4按需加载方式（three steps）
one step:
创建Bundle.js文件,这个文件其实是个通过bundle-loader包装后的组件来使用，下面会具体讲这个东西。
import React from 'react';
import PropTypes from 'prop-types';
class Bundle extends React.Component {
state = {
// short for "module" but that's a keyword in js,so "mod"
mod: null
}
componentWillMount() {
// 加载初始状态
this.load(this.props);
}
componentWillReceiveProps(nextProps) {
if (nextProps.load !== this.props.load) {
this.load(nextProps);
}
}
load(props) {
// 重置状态
this.setState({
mod: null
});
// 传入组件的组件
props.load((mod) => {
this.setState({
// handle both es imports and cjs
mod: mod.default ? mod.default : mod
});
});
}
render() {
// if state mode not undefined,The container will render children
return this.state.mod ? this.props.children(this.state.mod) : null;
}
}
Bundle.propTypes = {
load: PropTypes.func,children: PropTypes.func
};
export default Bundle;
second step:
import aContainer from 'bundle-loader?lazy!./containers/A'
const A = (props) => (
<Bundle load={aContainer}>
//这里只是给this.props.child传一个方法，最后在Bundle的render里面调用
{(Container) => <Container {...props}/>}
</Bundle>
)
third step:
render() {
return (
<div>
<h1>Welcome!</h1>
<Route path="/about" component={About}/>
<Route path="/dashboard" component={A}/>
</div>
)
}
3.router4按需加载方方式解析
(1).首先解释一下按需加载，通俗的将就是我当前的location在Home,那么我只应该加载Home的东西，而不应该去加载About等等其他的。
(2).Bundle.js这个文件的作用
先看这段代码：
module.exports = function (cb) {
__webpack_require__.e/* require.ensure */(2).then((function (require) {
cb(__webpack_require__(305));
}).bind(null,__webpack_require__)).catch(__webpack_require__.oe);
};
这里是我们通过import loadDashboard from 'bundle-loader?lazy!./containers/A'这种方式引入的container控件。我们使用了bundle-loader将A的源码转化成了上面的代码，具体实现大家可以看bundle-loader源码，代码很少。
上面说到Bundle.js其实就使用来处理这个文件的，这个文件需要一个callback的参数，在Bundle的load方法中，我们会设置这个callback，当路由要调到A Container这里的时候，就回去加载A Container,然后调用这个callback，这个callback会调用setState方法，将我们之前传入的load设置给mod，然后渲染出来。
4.webpack进行bundle-loader统一配置
这里匹配的是src/routers/下面的containers文件夹下面所有的js文件，包括二级目录。
{
// 匹配routers下面所有文件
// ([^/]+)\/?([^/]*) 匹配xxx/xxx 或者 xxx
test: /containers\/([^/]+)\/?([^/]*)\.jsx?$/,include: path.resolve(__dirname,'src/routers/'),// loader: 'bundle-loader?lazy'
loaders: ['bundle-loader?lazy','babel-loader']
}
5.部分源码
1.bundle-loader的源码
/*
MIT License http://www.opensource.org/licenses/mit-license.PHP
Author Tobias Koppers @sokra
*/
var loaderUtils = require("loader-utils");
module.exports = function() {};
module.exports.pitch = function(remainingRequest) {
this.cacheable && this.cacheable();
var query = loaderUtils.getOptions(this) || {};
if(query.name) {
var options = {
context: query.context || this.options.context,regExp: query.regExp
};
var chunkName = loaderUtils.interpolateName(this,query.name,options);
var chunkNameParam = "," + JSON.stringify(chunkName);
} else {
var chunkNameParam = '';
}
var result;
if(query.lazy) {
result = [
"module.exports = function(cb) {\n"," require.ensure([],function(require) {\n"," cb(require(",loaderUtils.stringifyRequest(this,"!!" + remainingRequest),"));\n"," }" + chunkNameParam + ");\n","}"];
} else {
result = [
"var cbs = [],\n"," data;\n","module.exports = function(cb) {\n"," if(cbs) cbs.push(cb);\n"," else cb(data);\n","}\n","require.ensure([]," data = require(",");\n"," var callbacks = cbs;\n"," cbs = null;\n"," for(var i = 0,l = callbacks.length; i < l; i++) {\n"," callbacks[i](data);\n"," }\n","}" + chunkNameParam + ");"];
}
return result.join("");
}
/*
Output format:
var cbs = [],data;
module.exports = function(cb) {
if(cbs) cbs.push(cb);
else cb(data);
}
require.ensure([],function(require) {
data = require("xxx");
var callbacks = cbs;
cbs = null;
for(var i = 0,l = callbacks.length; i < l; i++) {
callbacks[i](data);
}
});
*/
2.A的源码
import React from 'react';
import PropTypes from 'prop-types';
import * as reactRedux from 'react-redux';
import BaseContainer from '../../../containers/ReactBaseContainer';
class A extends BaseContainer {
constructor(props) {
super(props);
this.renderCustom = function renderCustom() {
return (
<div >
Hello world In A
</div>
);
};
}
render() {
// 返回父级view
return super.render();
}
}
A.propTypes = {
dispatch: PropTypes.func,};
function mapStateToProps(state) {
return { state };
}
export default reactRedux.connect(mapStateToProps)(A);
3.route.js的源码
import React from 'react';
import { BrowserRouter,Switch,Link } from 'react-router-dom';
import { Route } from 'react-router';
import PostContainer from '../containers/PostsContainer';
// 设置trunk文件的名字 the basename of the resource
import aContainer from './containers/A';
import bContainer from './containers/B';
import cContainer from './containers/C';
import Bundle from '../utils/Bundle';
const A = () => (
<Bundle load={aContainer}>
{Component => <Component />}
</Bundle>
)
const app = () =>
<div>
{/* path = "/about" */}
{/* "/about/" 可以，但"/about/1"就不可以了 exact 配置之后，需要路径绝对匹配,多个斜杠没有关系，这里直接在浏览器里面设置还有问题*/}
{/* path = "/about/" */}
{/* "/about/1" 可以，但"/about"就不可以了 用了strict，path要大于等于的关系，少一个斜杠都不行 */}
{/* exact 和 strick 都用了就必须一模一样，连斜杠都一样 */}
<Link to="/about/"> Link to about</Link>
<Route path="/" component={PostContainer} />
<Route path="/about/" component={A} />
{/* <Route path="/home" component={B} />
<Route component={C} /> */}
</div>
;
export default function () {
// 用来判断本地浏览器是否支持刷新
const supportsHistory = 'pushState' in window.history;
return (
<BrowserRouter forceRefresh={!supportsHistory} keyLength={12}>
<div>
{app()}
</div>
</BrowserRouter>
);
}
