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How to customize directives in Vue?

 Vue officially provides some commonly used instructions v-text, v-html, v-model, v-if, v-show, etc. In addition, Vue also allows developers to customize related instructions. It is divided into private custom directives and global custom directives. The difference between them is: in each vue component, private custom directives can be declared under the directives node, and private custom directives only take effect in this component; globally shared custom directives Defining a directive needs to be declared via Vue.directive().

Here's a practical example:

 <div id="app">
        <input type="text" v-bind:value="n">
        <br>
        focus:<input type="text" v-my-focus:value="n">
        N:<p v-text="n"></p>
        N:<p v-add="n"></p>
        <input type="text" v-add:value="n">
        <input type="text" v-add:value="n">
        <button @click="n++">click</button>
        <p>{{a}}</p>
    </div>

    <script>
     Vue.config.productionTip=false;
     //
     Vue.directive("my-focus", function(element,binding){
        element.focus();
    })
        var vm = new Vue({
            el: '#app',
            data: {
                n:10,
                a:undefined
            },
            methods: {},
            directives:{
                add(element,binding){
                    console.log(this);
                    console.log(element,binding);
                    // element.innerText=binding.value+100;
                    element.value=binding.value;
                }
                /* add:{
                    bind(element,binding){
                        console.log(this);
                    console.log(element,binding);
                    element.innerText=binding.value+100;
                    },
                    inserted(element,binding){
                        console.log(this);
                    console.log(element,binding);
                    element.innerText=binding.value+100;
                    },
                    update(element,binding){
                        console.log(this);
                    console.log(element,binding);
                    element.innerText=binding.value+100;
                    }
                } */
            }
        });
    </script>
Summary: 

  • bind: will only be called once, which means that it will be called when the instruction is bound to the element for the first time;
  • update: When the page data is updated, this function will be triggered; 
  • inserted: Called when the element where the instruction is located is inserted into the page.

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