Detailed explanation of usage of computed, filter, get, set
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>
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>
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>
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>
How to update the array with $set in vue.js
How to move the array in vue.js Position and update
Detailed graphic and text explanation of using vue2-highcharts in Vue
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