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intro-to-vue

最近喵了下 introducction to vue.js 视频感觉还不错，如果感兴趣，请戳。下面主要根据视频作者Sarah Drasner 的ppt 简单做下笔记，当然如果要系统过一遍的话还是推荐看官方文档。

最近喵了下 introducction to vue.js 视频感觉还不错，如果感兴趣，请戳。下面主要根据视频作者Sarah Drasner 的ppt 简单做下笔记，当然如果要系统过一遍的话还是推荐看官方文档。

Directives & Data Rendering

很多指令官方文档都有很详细的介绍，这里不多赘述。

NameShortcutPurposeExample
v-if,v-else-if,v-elsenoneConditional Rendering<g v-if="condition==='A'" /><g v-else-if="condition==='B'" /><g v-else />
v-bind:Bind attributes dynamically or pass props<div :style="{color: red}"></div>
v-on@Attaches an event listener to the element<button @click=""></button>
v-modelnoneCreates two-way binding，like combian withv-bind and v-on<input v-model="message" />
v-prenoneSkip compilling for raw content, can boost performance<div v-pre>row content with not methods</div>
v-shownoneWill show or hide the component/element based on state, but will leave it int the DOM without unmounting(unlike v-if)<child v-show="showComponent"></child>

Methods, Computed, Watch

methods

 methods: {
     addComment() {
         this.comments.push(this.newComment)
         this.newComment = ''
     }
 }

computed

Computed properties are calculations that will be cached and will only update when needed.Highly performant but use with understandin

computed: {
  filteredFilms() {
    let filter = new RegExp(this.filterText, 'i')
    return this.ratingsInfo.filter(el => el.title.match(filter))
  }
}

watch

Reactive programming is programming with asynchronous data streams. (响应式编程)

Vue.js, MobX or Ractive.js all use a variation of getters/setters. (对象原型链get,set方法)

Vue takes the object, walks through its properties and converts them to getter/setters

new Vue({
  data: {
    counter: 0
  }
})

Vue cannot detect property addition or deletion so we create this object to keep track

  1. Each component has a watcher instance.
  2. The properties touched by the watcher during the render are registered as dependencies
  3. When the setter is triggered, it lets the watcher know, and causes the component to re-render.

The Vue instance is the middleman between the DOM and the business logic

Watch updates the DOM only if it's required- performing calculations in JS is really performant but accessing the DOM is not. So we have a Virtual DOM which is like a copy, but parsed in JavaScript

It will only update the DOMfor things that need to be changed, which is faster.

watch {
    counter(value, oldValue) {
        console.log('The counter has changed')
    }
}

Components

int the short, A collection of elements that are encapsulated into a group that can be accessed through one single element.(节点，功能的集合)

template

Vue.js uses HTML-based template syntax to bind the Vue instance to the DOM, very useful for components.

Templates are optional, you can also write render functions with optional JSX support.

render function

<h1>blogTitle</h1>

render: function (createElement) {
  return createElement('h1', this.blogTitle)
}

用到的的时候喵下createElement 方法文档用法即可，

// @returns {VNode}
createElement(
  // {String | Object | Function}
  // 一个 HTML 标签名、组件选项对象，或者
  // resolve 了上述任何一种的一个 async 函数。必填项。
  'div',

  // {Object}
  // 一个与模板中属性对应的数据对象。可选。
  {
    // (详情见下一节)
  },

  // {String | Array}
  // 子级虚拟节点 (VNodes)，由 `createElement()` 构建而成，
  // 也可以使用字符串来生成“文本虚拟节点”。可选。
  [
    '先写一些文字',
    createElement('h1', '一则头条'),
    createElement(MyComponent, {
      props: {
        someProp: 'foobar'
      }
    })
  ]
)

data

Each component instancehas its own isolated scope, so data must be a function.

data() {
    return {
        counter: 0
    }
}

props

Passing data down from the parent to the child.(父组件传参给子组件)

props: [
    'prop1',
    'prop2'
]

or props have type & validation 

props: {
  text: [String, Number]
}

props: {
    text: {
        type: String,
        required: true,
        default: 'hello mr. magoo'
    }
}

Objects and Arrays need their defaults to be returned a function

props: {
    text: {
      type: Object,
      default() {
        return { message: 'hello mr. magoo' }
      }
    }
}

use static value

<child count="1"></child>

use the state of the parent, We use v-bindor : to dynamically bind props to data on the parent

<child :count="count"></child>

$emit

The child is reporting it's activity to the parent by $emit (子组件传值给父组件)

<child @myEvent="parentHandler"></child>

methods: {
  fireEvent() {
    this.$emit('myEvent', eventValueOne, eventValueTwo);
  }
}

slot

插槽，相对灵活，简单来说，就是定义一块html模板，由父组件决定是否显示，该怎么显示。

<script type="text/x-template" id="childarea">
  <div class="child">
    <slot></slot>
    <p>It's a veritable slot machine!<br> 
    Ha ha aw</p>
  </div>
</script>

<div id="app">
  <h2>We can use slots to populate content</h2>
  <app-child>
    <h3>This is slot number one</h3>
  </app-child>
  <app-child>
    <h3>This is slot number two</h3>
    <small>I can put more info in, too!</small>
  </app-child>
</div>

可以由默认插槽，匿名插槽

<slot>default slot</slot>

当然也可以有多个插槽，需要命名

<slot name="headerinfo"></slot>
<h1 slot="headerinfo">I will populate the headerinfo slot</h1>

也可以传数据，当然数据只能是子组件内部的数据，父组件提供样式。

<slot name="up" :data="data"></slot>

keep-alive

可以使被包含的组件保留状态，或避免重新渲染

<keep-alive include="a">
  <component>
    <!-- name 为 a 的组件将被缓存！ -->
  </component>
</keep-alive>

<keep-alive include="a">
  <component>
    <!-- 除了name 为 a 的组件将被缓存！ -->
  </component>
</keep-alive>

跟router结合，实现有的路由视图缓存，仅限单页面应用。

// routes 配置
export default [
  {
    path: '/',
    name: 'home',
    component: Home,
    meta: {
      keepAlive: true // 需要被缓存
    }
  }, {
    path: '/:id',
    name: 'edit',
    component: Edit,
    meta: {
      keepAlive: false // 不需要被缓存
    }
  }
]

<keep-alive>
    <router-view v-if="$route.meta.keepAlive">
        <!-- 这里是会被缓存的视图组件，比如 Home！ -->
    </router-view>
</keep-alive>

<router-view v-if="!$route.meta.keepAlive">
    <!-- 这里是不被缓存的视图组件，比如 Edit！ -->
</router-view>

Filters, Mixins, Directive, & Plugin

filters

The first thing to understand about filters is that they aren't replacements for methods, computed values, or watchers, because filters don't transform the data, just the output that the user sees.(过滤器不转换数据，只过滤输出)

Two ways to register a new filter:

//global
Vue.filter('filterName', function(value,arg1,arg2) {
  return // thing to transform
});
 
//locally, like methods or computed
filters: {
  filterName(value,arg1,arg2) {
    return // thing to transform
  }
}

// use
:="data | filterA | filterB(arg1,arg2)"

mixins

这是一种常见的情况:您有两个非常相似的组件，它们共享相同的基本功能，但是它们之间有足够多的不同之处，因此您面临一个十字路口:我要将这个组件分成两个不同的组件吗?或者我保留一个组件，但创建足够的变化与道具，我可以改变每一个。

mixin允许您封装一项功能，以便可以在整个应用程序的不同组件中使用它。

//modal
const Modal = {
  template: '#modal',
  data() {
    return {
      isShowing: false
    }
  },
  methods: {
    toggleShow() {
      this.isShowing = !this.isShowing;
    }
  },
  components: {
    appChild: Child
  }
}

//tooltip
const Tooltip = {
  template: '#tooltip',
  data() {
    return {
      isShowing: false
    }
  },
  methods: {
    toggleShow() {
      this.isShowing = !this.isShowing;
    }
  },
  components: {
    appChild: Child
  }
}

可以看到冗余的代码片段可以封装起来，改写后如下，

const toggle = {
  data() {
    return {
      isShowing: false
    }
  },
  methods: {
    toggleShow() {
      this.isShowing = !this.isShowing;
    }
  }
}

const Modal = {
  template: '#modal',
  mixins: [toggle],
  components: {
    appChild: Child
  }
};

const Tooltip = {
  template: '#tooltip',
  mixins: [toggle],
  components: {
    appChild: Child
  }
};

默认情况下，mixin 将首先应用，然后应用component，这样我们就可以根据需要覆盖它。

//mixin
const hi = {
  mounted() {
    console.log('hello from mixin!')
  }
}

//vue instance or component
new Vue({
  el: '#app',
  mixins: [hi],
  mounted() {
    console.log('hello from Vue instance!')
  }
});

//Output in console
//> hello from mixin!
//> hello from Vue instance!

//mixin
const hi = {
  methods: {
    sayHello: function() {
      console.log('hello from mixin!')
    }
  },
  mounted() {
    this.sayHello()
  }
}

//vue instance or component
new Vue({
  el: '#app',
  mixins: [hi],
  methods: {
    sayHello: function() {
      console.log('hello from Vue instance!')
    }
  },
  mounted() {
    this.sayHello()
  }
})

// Output in console
//> hello from Vue instance!
//> hello from Vue instance!

Global Mixins 会应用于每一个组件，不过一般很少用到

Vue.mixin({
  mounted() {
    console.log('hello from mixin!')
  }
})

new Vue({
  ...
})

directive

v-if， v-bind 这些都是内置的指令，当然我们可以根据自己需要自定义指令

Vue.directive('tack', {
 bind(el, binding, vnode) {
    el.style.position = 'fixed'
  }
});

<p v-tack>I will now be tacked onto the page</p>

当然指令也可以接收参数值

v-example="string"， 这将使用字符串作为表达式。

<div v-if="stateExample">I will show up 
if stateExample is true</div>

<p v-html="'<strong>this is an example of a string
 in some text</strong>'"></p>

v-example:arg="value"，这允许我们向指令传递一个参数。在下面的示例中，我们将绑定到一个类，并使用一个单独存储的对象对其进行样式设置。

<div v-bind:class="someClassObject"></div>

v-example:arg.modifier="value" ，这允许我们使用修饰符。下面的示例允许我们在单击事件上调用preventDefault()。

<button v-on:submit.prevent="onSubmit"></button>

传递一个参数

<p v-tack:left="70">I'll now be offset from the left instead of the top</p>

Vue.directive('tack', {
  bind(el, binding, vnode) {
    el.style.position = 'fixed';
    const s = (binding.arg == 'left' ? 'left' : 'top');
    el.style[s] = binding.value + 'px';
  }
});

传递多个参数

<p v-tack="{ top: '40', left: '100' }">Stick me 40px from the top of the
page and 100px from the left of the page</p>

Vue.directive('tack', {
  bind(el, binding, vnode) {
    el.style.position = 'fixed';
    el.style.top = binding.value.top + 'px';
    el.style.left = binding.value.left + 'px';
  }
});

plugin

插件通常用来为 Vue 添加全局功能。插件的功能范围没有严格的限制——一般有下面几种：

  1. 添加全局方法或者属性。如：vue-custom-element
  2. 添加全局资源：指令/过滤器/过渡等。如 vue-touch
  3. 通过全局混入来添加一些组件选项。如 vue-router
  4. 添加 Vue 实例方法，通过把它们添加到 Vue.prototype 上实现。
  5. 一个库，提供自己的 API，同时提供上面提到的一个或多个功能。如 vue-router

使用

// 调用 `MyPlugin.install(Vue)`
Vue.use(MyPlugin, { someOption: true })

new Vue({
  // ...组件选项
})

开发

MyPlugin.install = function (Vue, options) {
  // 1. 添加全局方法或属性
  Vue.myGlobalMethod = function () {
    // 逻辑...
  }

  // 2. 添加全局资源
  Vue.directive('my-directive', {
    bind (el, binding, vnode, oldVnode) {
      // 逻辑...
    }
    ...
  })

  // 3. 注入组件选项
  Vue.mixin({
    created: function () {
      // 逻辑...
    }
    ...
  })

  // 4. 添加实例方法
  Vue.prototype.$myMethod = function (methodOptions) {
    // 逻辑...
  }
}

Vue CLI

使用构建工具，可以让我们更方便的编写组件，并且使用es6 等语法。

yarn global add @vue/cli @vue/cli-service-global
vue create project or vue ui
cd project
yarn
vue serve or yarn run dev

简单的.vue 模板组件

<template>
  <div>
     <!-- Write your HTML with Vue in here -->  
  </div>
</template>

<script>
  export default {
     // Write your Vue component logic here
  }
</script>

<style scoped>
  /* Write your styles for the component in here */
</style>

引入组件

<new></new>

import New from './components/New.vue';
export default {
  components: {
    New
  }
}

也可以给组件取别名

<app-new></app-new>

import New from './components/New.vue';
export default {
  components: {
    appNew: New
  }
}

Vue Router & NUXT

Vue Router

官方文档很详细了，这里不多叙述

NUXT

服务端渲染，不需要定义路由视图，

Vuex

组件数量如果比较多，组件之间可能不存在父子组件的关系，这时候就要引入状态管理的机制了。

export const store = new Vuex.Store({
  state: {
    counter: 0
  },
  //showing things, not mutating state
  getters: {
    tripleCounter: state => {
      return state.counter * 3;
    }
  },
  //mutating the state
  //mutations are always synchronous
  mutations: {
    //showing passed with payload, represented as num
    increment: (state, num) => {
      state.counter += num;
    }
  }, 
  //commits the mutation, it's asynchronous
  actions: {
    // showing passed with payload, represented as asynchNum (an object)
    asyncIncrement: ({ commit }, asyncNum) => {
      setTimeout(() => {
        //the asyncNum objects could also just be static amounts
        commit('increment', asyncNum.by);
      }, asyncNum.duration);
    },
    async actionA ({ commit }) {
        commit('gotData', await getData())
     },
     async actionB ({ dispatch, commit }) {
        await dispatch('actionA') // 等待 actionA 完成
        commit('gotOtherData', await getOtherData())
     }
  }
});

在组件本身上，我们将使用computed for getters(这是有意义的，因为这个值已经为我们计算过了)，使用commit访问mutations的方法，以及使用dispatch访问actions的方法

computed: {
  value() {
    return this.$store.getters.tripleCounter;
  }
},
methods: {
  increment() {
    this.$store.commit('increment', 2)
  },
  asyncIncrement() {
    this.$store.dispatch('asyncIncrement', 2)
  }
}

使用spred opetrator

computed: {
  localComputed () { /* ... */ },
  // 使用对象展开运算符将此对象混入到外部对象中
  ...mapState({
    // ...
  })
},
methods: {
    ...mapActions([
      // map this.increment() to this.$store.commit('increment')
      'increment', 
      'decrement',
      'asyncIncrement'
    ])
  }

注意，mutations 必须是同步函数，actions 支持异步操作

多模块

const moduleA = {
  state: { ... },
  mutations: { ... },
  actions: { ... },
  getters: { ... }
}

const moduleB = {
  state: { ... },
  mutations: { ... },
  actions: { ... }
}

const store = new Vuex.Store({
  modules: {
    a: moduleA,
    b: moduleB
  }
})

store.state.a // -> moduleA 的状态
store.state.b // -> moduleB 的状态

Composition API

VUE3 引入的新特性，composition-api-introduction

当然VUE2也可以使用，

npm i @vue/composition-api -S

以前vue2的时候，组件结构规范，比如data() 声明数据变量，methods 声明方法，这样的结构当然有看起来当然结构清晰，但是另一方面，会导致数据变量分散开来，因为这个原因，vue又引发魔法的this的，使得组件里面属性里面的this总是指向当前组件。

引入Composition API的，相当于就把方法，变量等组件属性抽离出来，形成一个整体的功能函数，按需载入，返回所需，它们不会修改或改变函数范围之外的东西，所以在多次执行时，总是会可靠地接收到相同的值和相同的输入；当然对typescript也支持更好，毕竟vue3才有typescript重写，同时消除了让人困惑的魔法this

下面举个简单例子，

Components写法

const App = {
    data() {
        return {
            count: 0
        }
    },
    props: { 
      countA: {
        type: Number,
        required: true
      }
    },
    mounted(){
      console.log('component is mounted!')
    }
    methods: {
        increment: function() {
            this.count++;
            console.info(this.count)
        }
    }
}

Composition API 写法

const { ref, reactive, computed } = Vue
const App = {
   props: { 
      countA: {
        type: Number,
        required: true
      }
    },
    setup(props, context) {
        const count = ref(0)
        const state = reactive({
            count: 0,
            double: computed(() => state.count * 2)
        })
        watch(state, (newValue, oldValue) => {
            console.log(newValue.count)
        })
        watchEffect(() => {
            console.log(state.count)
        })
        onMounted(() => {
          console.log('component is mounted!')
        })
        function increment() {
            count.value++
            state.count++;
            console.info(count.value)
            console.info(state.count)
            console.info(props.countA)
        }
        context.emit('eventName')
        return {
             count,
            // state
            ...toRefs(state)
             increment
        }
    }
}

Single File Components <script setup>

<script setup>
  const state = reactive({
    count: 0
  })

  onMounted(() => {
    console.log(state.count)
  })

  return {
    state
  }
</script>

相关链接

frontendmaster: introction to vue.js

github: sdras intro-to-vue

vue.js org

github:nuxt

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java-common-mistakes

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