【问题描述】

一位朋友遇到这么一个开发场景：在表格里面嵌入el-select组件，每次修改值后，失去焦点时将修改值提交后台保存，但是发现在el-select组件失去焦点时，blur事件的evt.target.value值总为前一次选择的值；

【问题摘要】

1、el-select组件失去焦点时需要获取组件当前值而不是上一次的值；

2、el-select组件切换选项时不提交后台，只有当组件失去焦点后才提交当前值；

【分析问题】

一刚开始以为是下拉框收起动画延时问题导致内部value值被延时修改，所以就在blur事件里延时获取evt.target.value,貌似没问题了

blurHandler(evt){setTimeout(() => {console.log(evt.target.value);},250)
},

随后又发现通过@blur绑定事件只会触发一次，好吧那就加修饰符吧：@blur.capture.native，好像解决只触发一次的问题了

<el-select v-model="value" @blur.capture.native="nativeBlurHandler" ref="select"><el-optionv-for="item in options":key="item.value":label="item.label":value="item.value"></el-option>
</el-select>

但是随之而来的问题就是，每次切换取值后都会触发一次blur事件，这可不是我们想要的，这不变成change事件了吗？继续深挖！

那就打印一下this.$refs.select看看吧，找到this.$refs.select.$data, 看里面有定义啥变量没,发现了如下变量：

log(eventName){let {createdSelected,inputHovering,isOnComposition,isSilentBlur,menuVisibleOnFocus,softFocus,visible} = this.$refs.select.$data;console.table([{name: eventName,value: '',},// {// 	name: 'createdSelected',// 	value: createdSelected// },{name: 'inputHovering',value: inputHovering},// {// 	name: 'isOnComposition',// 	value: isOnComposition// },{name: 'isSilentBlur',value: isSilentBlur},// {// 	name: 'menuVisibleOnFocus',// 	value: menuVisibleOnFocus// },// {// 	name: 'softFocus',// 	value: softFocus// },{name: 'visible',value: visible},])
}

通过反复测试发现只有inputHovering，isSilentBlur，visible这三个变量与el-select组件的focus,blur事件有关联：

通过上图可以发现，只有最下方的失去焦点事件才是我们想要的，此时visible==false，isSilentBlur==true,正好满足我们的判断条件,于是blur事件改造成这样了：

nativeBlurHandler(evt){console.log('nativeBlurHandler', {...this.$refs.select});let {isSilentBlur,visible} = this.$refs.select;if( isSilentBlur  && !visible ) {console.log('提交', this.$refs.select.selected.currentValue);}this.log('blur事件');
},

又因为value取值从evt.target.value获取的不是实时的，也就是值不正确，继续深挖，发现this.$refs.select.selected.currentValue就是我们想要的正确的值，于是乎，问题就解决了！测试demo完整代码如下：

【完整Test代码】

<!DOCTYPE html>
<html><head><meta charset="UTF-8"><!-- import CSS --><link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/index.css"></head><body><div id="app"><el-select v-model="value" placeholder="请选择" @blur="blurHandler" @blur.capture.native="nativeBlurHandler" ref="select"><el-optionv-for="item in options":key="item.value":label="item.label":value="item.value"></el-option></el-select></div></body><!-- import Vue before Element --><script src="https://unpkg.com/vue@2/dist/vue.js"></script><!-- import JavaScript --><script src="https://unpkg.com/element-ui/lib/index.js"></script><script>let selectElm;new Vue({el: '#app',data: function() {return {options: [{value: '黄金糕',label: '黄金糕'}, {value: '双皮奶',label: '双皮奶'}, {value: '蚵仔煎',label: '蚵仔煎'}, {value: '龙须面',label: '龙须面'}, {value: '北京烤鸭',label: '北京烤鸭'}],value: ''}},methods: {focusHandler(evt){this.log('focus事件');},blurHandler(evt){setTimeout(() => {console.log(evt.target.value);},250)},nativeBlurHandler(evt){console.log('nativeBlurHandler', {...this.$refs.select});let {isSilentBlur,visible} = this.$refs.select;if( isSilentBlur && !visible ) {console.log('提交', this.$refs.select.selected.currentValue);}this.log('blur事件');},log(eventName){let {createdSelected,inputHovering,isOnComposition,isSilentBlur,menuVisibleOnFocus,softFocus,visible} = this.$refs.select.$data;console.table([{name: eventName,value: '',},// {// 	name: 'createdSelected',// 	value: createdSelected// },{name: 'inputHovering',value: inputHovering},// {// 	name: 'isOnComposition',// 	value: isOnComposition// },{name: 'isSilentBlur',value: isSilentBlur},// {// 	name: 'menuVisibleOnFocus',// 	value: menuVisibleOnFocus// },// {// 	name: 'softFocus',// 	value: softFocus// },{name: 'visible',value: visible},])}}})</script>
</html>

【封装自定义指令】

想到给组件添加ref实际并不是那么好用且麻烦，所以我又将其封装成了指令，指令代码及用法如下，大家随取随用哈↓↓↓↓↓↓

<!DOCTYPE html>
<html><head><meta charset="UTF-8"><!-- import CSS --><link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/index.css"></head><body><div id="app"><el-row><el-col :span="24"><el-select v-select-blur="selectBlurHandler" v-model="value"><el-option v-for="item in options" :key="item.value" :label="item.label" :value="item.value"></el-option></el-select></el-col></el-row></div></body><!-- import Vue before Element --><script src="https://unpkg.com/vue@2/dist/vue.js"></script><!-- import JavaScript --><script src="https://unpkg.com/element-ui/lib/index.js"></script><script>Vue.directive('select-blur', {bind: function(el, binding, vnode) {const selectComponent = vnode.componentInstance;if( selectComponent.$options.name === 'ElSelect' ) {selectComponent.$watch('visible', (n,o) => {const {isSilentBlur,visible,} = selectComponent;if(isSilentBlur && !visible) {selectComponent.handleBlur();}})selectComponent.$on('blur', () => {let {visible,selected: {currentValue}} = selectComponent;if (!visible) {binding?.value && typeof binding.value === 'function' && binding.value(currentValue);selectComponent.blur();    //处理页面频繁聚焦失焦导致重复触发blur事件的问题}}, true);}},unbind: function(el, binding, vnode) {const selectComponent = vnode.componentInstance;if( selectComponent.$options.name === 'ElSelect' ) {selectComponent.$off('blur');}}});const app = new Vue({el: '#app',data: function() {return {options: [{value: '黄金糕',label: '黄金糕'}, {value: '双皮奶',label: '双皮奶'}, {value: '蚵仔煎',label: '蚵仔煎'}, {value: '龙须面',label: '龙须面'}, {value: '北京烤鸭',label: '北京烤鸭'}],value: ''}},methods: {selectBlurHandler(val) {console.log('提交', val);},}})</script>
</html>