vue router

参考：

　　https://router.vuejs.org/zh-cn/advanced/lazy-loading.html

路由懒加载

// 配置文件
module.exports = {
    entry: {
        index: './index.js',
    },
    output: {
        path: __dirname + "/dist",
        filename: "[name].js",
        publicPath:"./dist/"
    },
    devtool: 'eval-source-map',
    module: {
        rules: [
            {
                test: /.vue$/,
                loader: 'vue-loader'
            },
            {
                test: /(.jsx|.js)$/,
                use: {
                    loader: "babel-loader",
                    options: {
                        presets: ["es2015"],
                        plugins: ["syntax-dynamic-import"]
                    }
                },
                exclude: /node_modules/
            }
        ]
    },
    resolve: {
        extensions: [".vue",".js",".json"],
        alias: {
            'vue$': 'vue/dist/vue.js',
        }
    }
};

// ./routers/uA.vue
<template>
    <div>
        aaaaaaaaaaa
    </div>
</template>

<script>
    export default {
        name: "v-a"
    }
</script>
<style scoped></style>

// ./routers/uB.vue
<template>
    <div>
        bbbbbbbbbbb
    </div>
</template>

<script>
    export default {
        name: "v-b"
    }
</script>
<style scoped></style>

// index.js
import VueRouter from "vue-router"
import Vue from "vue"

const vA = ()=> import('./routers/vA')
const vB = ()=> import('./routers/vB')

const router = new VueRouter({
    routes: [
        { path: '/a', component: vA },
        { path: '/b', component: vB }
    ]
})
Vue.use(VueRouter)
new Vue({
    el:"#root",
    router:router
});

// main.html
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <div id="root">
        <router-link to="/a">Go to a</router-link>
        <router-link to="/b">Go to b</router-link>
        <router-view></router-view>
    </div>
</body>
<script src="dist/index.js"></script>
</html>

// 依赖
  "devDependencies": {
    "babel-core": "^6.26.0",
    "babel-loader": "^7.1.2",
    "babel-plugin-syntax-dynamic-import": "^6.18.0",
    "babel-preset-es2015": "^6.24.1",
    "css-loader": "^0.28.8",
    "style-loader": "^0.19.1",
    "vue": "^2.5.13",
    "vue-loader": "^13.6.2",
    "vue-router": "^3.0.1",
    "vue-template-compiler": "^2.5.13",
    "webpack": "^3.10.0"
  }

View Code

仅当这个路由组件第一次需要被显示的时候，才会下载这个组件。打包后dist出现这几个文件:

0和1代表被异步加载的路由组件。

如果手误，import一个vue-loader，则会报如下错误：

WARNING in ./node_modules/vue-loader/lib/utils/try-require.js
12:11-27 Critical dependency: the request of a dependency is an expression
@ ./node_modules/vue-loader/lib/utils/try-require.js
@ ./node_modules/vue-loader/lib/loader.js
@ ./node_modules/vue-loader/index.js
@ ./index.js

ERROR in ./node_modules/resolve/lib/async.js
Module not found: Error: Can't resolve 'fs' in 'C:UsersMRLWJDesktop est outer ode_modules esolvelib'
@ ./node_modules/resolve/lib/async.js 2:9-22
@ ./node_modules/resolve/index.js
@ ./node_modules/vue-loader/lib/utils/try-require.js
@ ./node_modules/vue-loader/lib/loader.js
@ ./node_modules/vue-loader/index.js
@ ./index.js

Api

关于路由守卫：https://router.vuejs.org/zh-cn/advanced/navigation-guards.html

this.$router.push('/qwe')：

　　修改路由为 #/qwe（路由组件会切换），不发出请求

router.onReady

　　回调函数被调用的时候，就意味着当前要显示的（同步或者异步）路由组件已经准备好了，这时这个路由组件还没有完成挂载（onReady的回调函数在组件beforeCreate前执行）。

router.beforeEach

　　在路由切换前执行（页面打开时也会执行一次），回调函数中需要调用next（），否则路由不切换。可以注册多个，会按次序执行，上一个没有执行next的话，下一个不会执行，路由不会切换，当最后一个执行了next时，路由才开始切换（组件开始挂载）

文档中提示的触发流程如下：

Navigation triggered.
Call leave guards in deactivated components.
Call global beforeEach guards.
Call beforeRouteUpdate guards in reused components (2.2+).
Call beforeEnter in route configs.
Resolve async route components.
Call beforeRouteEnter in activated components.
Call global beforeResolve guards (2.5+).
Navigation confirmed.
Call global afterEach hooks.
DOM updates triggered.
Call callbacks passed to next in beforeRouteEnter guards with instantiated instances.

以上流程中，只要next没执行，就不会到下一步，如进行以下设置：

beforeRouteEnter(to,form,next){
    setTimeout(()=>{
        next()
    },2000)
}

则全局的beforeResolve会等待以上的next执行后执行。

切换路由，组件由A->B时：

在路由中，component reused 的意思是路由没有发生变化，而仅仅参数发生了变化（user/1 -> user/2），这时组件中的钩子 beforeRouteUpdate会执行。