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Vue中$refs的理解.md

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Understanding $refs in Vue

$refs is an object that holds all the DOM elements and component instances that have been registered with the ref attribute.

Description

ref is used to register reference information for elements or child components. The reference information will be registered on the $refs object of the parent component. If used on a regular DOM element, the reference points to the DOM element. If used on a child component, the reference points to the component instance. Additionally, when v-for is used on an element or component, the reference information will be an array containing DOM nodes or component instances.

<!DOCTYPE html>
<html>
<head>
    <title>Vue</title>
</head>
<body>
    <div id="app">
        <div ref="node">Node</div>
        <layout-div ref="layout"></layout-div>
        <div v-for="i in 3" :key="i" ref="nodearr">{{i}}</div>
    </div>
</body>
<script src="https://cdn.bootcss.com/vue/2.4.2/vue.js"></script>
<script type="text/javascript">
    Vue.component("layout-div", {
      data: function(){
          return {
            count: 0
          }
      },
      template: `<div>
                    <div>{{count}}</div>
                </div>`
    })

    var vm = new Vue({
        el: '#app',
        mounted: function(){
            console.log(this.$refs.node); // <div>Node</div> // DOM element
            console.log(this.$refs.layout); // VueComponent {_uid: 1, ...} // component instance
            console.log(this.$refs.nodearr); // (3) [div, div, div] // array of DOM elements
        }
    })
</script>
</html>

Because ref itself is created as a rendering result and cannot be accessed during initial rendering, and $refs is not reactive, you should not attempt to use it for data binding in the template. When accessing ref during initialization, it should be called in the mounted method of its lifecycle. After data update, the $nextTick method should be used to pass the callback operation to obtain elements or instances. Additionally, direct manipulation of DOM elements is not recommended, it is preferable to use data binding to let the ViewModel of the MVVM handle DOM operations.

<!DOCTYPE html>
<html>
<head>
    <title>Vue</title>
</head>
<body>
    <div id="app"></div>
</body>
<script src="https://cdn.bootcss.com/vue/2.4.2/vue.js"></script>
<script type="text/javascript">
var vm = new Vue({
    el: '#app',
    data: function(){
        return {
            msg: 0
        }
    },
    template:  `<div>
                   <div ref="node">{{msg}}</div>
                   <button @click="updateMsg">button</button>
                </div>`,
    beforeMount: function(){
        console.log(this.$refs.node); // undefined
    },
    mounted: function(){
        console.log(this.$refs.node); // <div>0</div>
    },
    methods: {
        updateMsg: function(){
            this.msg = 1;
            console.log(this.$refs.node.innerHTML); // 0
            this.$nextTick(() => {
                console.log(this.$refs.node.innerHTML); // 1
            })
        }
    }
})
</script>
</html>

Daily Question

https://github.com/WindrunnerMax/EveryDay

Reference

https://cn.vuejs.org/v2/api/#ref
https://zhuanlan.zhihu.com/p/50638655
https://juejin.im/post/5da58c54e51d4524e207fb92