Detailed explanation of usage of computed, filter, get, set-JS Tutorial-php.cn

Detailed explanation of usage of computed, filter, get, set

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Release： 2018-03-28 15:04:37

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This time I will bring you a detailed explanation of the usage of computed, filter, get, and set. What are the precautions when using computed, filter, get, and set. The following is a practical case, let's take a look.

1. The computed method of vue.js:

handles complex logic, based on dependency caching, and will re-value when dependencies change. . The same effect can be achieved using methods, but methods will be re-invoked and executed when re-rendering. Computed is better than methods in terms of performance. Methods can be used when caching is not needed.

Example 1: computed and methods implement flippingString##

<template>
 <p>
 <input v-model="message">
 <p>原始字符串: {{ message }}</p>
 <p>计算后反转字符串: {{ reversedMessage }}</p>
 <p>使用方法后反转字符串: {{ reversedMessage2() }}</p>
 </p>
</template>
<script>
export default {
 data () {
 return {
 message: 'Runoob123!'
 }
 },
 computed: {
 // 计算属性的 getter
 reversedMessage: function () {
 // `this` 指向 vm 实例
 return this.message.split('').reverse().join('')
 }
 },
 methods: {
 reversedMessage2: function () {
 return this.message.split('').reverse().join('')
 }
 }
}
</script>

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Execution result:

Example 2: Computed get() and set() usage

<template>
 <p>
 	<select v-model="site">
 		<option value="Google http://www.google.com">Google http://www.google.com</option>
 		<option value="baidu http://www.baidu.co">baidu http://www.baidu.com</option>
 		<option value="网易 http://www.163.com">网易 http://www.163.com</option>
 	</select>
 	<p>name：{{name}}</p>
 	<p>url：{{url}}</p>
 </p>
</template>
<script>
export default {
 data () {
 return {
 name: 'Google',
 url: 'http://www.google.com'
 }
 },
 computed: {
 site: {
 // getter
 get: function () {
 return this.name + ' ' + this.url
 },
 // setter
 set: function (newValue) {
 let names = newValue.split(' ')
 this.name = names[0]
 this.url = names[names.length - 1]
 }
 }
 }
}
</script>

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Execution results:

2. filterfilter method of vue.js:

The filter will return data A simple function that performs processing and returns the processing result. However, it was removed in the vue2.0 version. The alternative is to write the function in methods.

Instance:

<template>
 <p>
 <input v-model="filterText"/>
 <ul>
 <li v-for="item in obj">
 <span>{{myfilter(item.label)}}</span>
 </li>
 </ul>
 </p>
</template>
<script>
export default {
 data () {
 return {
 obj: [
 {value: 0, label: 'beijing'},
 {value: 1, label: 'shanghai'},
 {value: 2, label: 'guangdong'},
 {value: 3, label: 'zhejiang'},
 {value: 4, label: 'jiangshu'}
 ],
 filterText: ''
 }
 },
 methods: {
 myfilter (value) {
 if (value.indexOf(this.filterText) > -1) {
 return value
 }
 }
 }
}
</script>

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Execution result:

3, vue.js The get and set methods:

The data attribute in vue can respond to data changes. Internally, the data attribute is converted into getter/setter. In vue2.0, get() and set( ) is used in computed properties and has been covered in the computed example above. In addition, vm.$set(

object, key, value) inherited from vue1.0 is used to dynamically monitor data elements. After the instance is created, the array attribute is added and a response is available. method implementation.

<template>
 <p>
 <input v-model="opt" @blur="add()"/>
 <ul>
 <li v-for="item in arr">
 {{ item }}
 </li>
 </ul>
 </p>
</template>
<script>
export default {
 data () {
 return {
 arr: [ '北京', '上海', '广东', '深圳' ],
 opt: ''
 }
 },
 methods: {
 add () {
 this.$set(this.arr, this.arr.length, this.opt)
 }
 }
}
</script>

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Execution results:

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!