最近在看element-ui的源码，发现了一个这样的属性:inject.遂查看官网provider/inject

provider/inject：简单的来说就是在父组件中通过provider来提供变量，然后在子组件中通过inject来注入变量。

需要注意的是这里不论子组件有多深，只要调用了inject那么就可以注入provider中的数据。而不是局限于只能从当前父组件的prop属性来获取数据。

下面我们来验证下猜想：

• first：定义一个parent component

<template>
  <div>
<childOne></childOne>
  </div>
</template>

<script>
  import childOne from '../components/test/ChildOne'
  export default {
    name: "Parent",
    provide: {
      for: "demo"
    },
    components:{
      childOne
    }
  }

在这里我们在父组件中provide for这个变量。

• second 定义一个子组件

<template>
  <div>
    {{demo}}
    <childtwo></childtwo>
  </div>
</template>

<script>
  import childtwo from './ChildTwo'
  export default {
    name: "childOne",
    inject: ['for'],
    data() {
      return {
        demo: this.for
      }
    },
    components: {
      childtwo
    }
  }
</script>

• third 定义另一个子组件

<template>
  <div>
    {{demo}}
  </div>
</template>

<script>
  export default {
    name: "",
    inject: ['for'],
    data() {
      return {
        demo: this.for
      }
    }
  }
</script>

在2个子组件中我们使用jnject注入了provide提供的变量for，并将它提供给了data属性。

这里官网注明例子只工作在 Vue 2.2.1 或更高版本。低于这个版本时，注入的值会在 props 和 data 初始化之后得到。

运行之后看下结果

从上面这个例子可以看出，只要在父组件中调用了，那么在这个父组件生效的生命周期内，所有的子组件都可以调用inject来注入父组件中的值。

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