This time I will bring you a summary of the use of vue's built-in instructions. What are the precautions when using vue's built-in instructions. The following is a practical case, let's take a look.
Directives are special attributes with v- prefix. Their responsibility is to reactively apply the associated effects to the DOM when the value of the expression changes.
Built-in instructions
1. v-bind: respond to and update DOM characteristics; for example: v-bind:href v-bind:class v-bind:title etc.
The main usage is to bind attributes and dynamically update the attributes on HTML elements;
<a v-bind:href="url" rel="external nofollow" rel="external nofollow" >...</a>
<!-- 缩写 -->
<a :href="url" rel="external nofollow" rel="external nofollow" >...</a>
<p :title='title'>标题</p>
var app = new Vue({
el: '#app',
data: {
url: 'www.baidu.com',
title: 'bind'
},
}）2, v-on: used for monitoring DOM events; For example: v-on:click v-on:keyup
By the way, let’s talk about the methods and events
2.1 The expression of @click The formula can use JavaScript statements directly, or it can be a function name in the methods option in the Vue instance. Parameters can be passed in the method
<!-- 完整语法 -->
<a v-on:click="doSomething">...</a>
<!-- 缩写 -->
<a @click="doSomething()">...</a> //是一个方法名
<p ng-if='show'>一段文本</p>
<button @click="show=false">点击隐藏文本</button> //直接是一个内联的语句
<button v-on:click="count++">Add 1</button>
var app = new Vue({
el: '#app',
data:{
show: true，
counter： 0
},
methods: {
doSomething: function(){
console.log(this.title);
},
}
}）2.2 Methods and events:
Vue provides a special variable $event, which is used to access native DOM events, which can prevent events from bubbling or prevent links from opening.
Write an example to prevent bubbling:
<p @click="stopClick1('stop1',$event)">
<p @click="stopClick2('stop2',$event)">
<p @click="stopClick3('stop3',$event)">阻止冒泡</p>
</p>
</p>
</p>
methods:{
stopClick3: function(message, event){
console.log(message);
event.stopPropagation(); //阻止冒泡
},
stopClick2: function(message, event){
console.log(message);
},
stopClick1: function(message, event){
console.log(message);
}
}2.3 Modification Symbol:
Add a small dot "." after the @bound event, and then follow it with a suffix to use the modifier.
The above bubbling event can be written as a direct user modifier:
<p @click.stop="stopClick3('stop3')">阻止冒泡</p> //不用通过$event事件再来写了
Some commonly used modifiers are:
• .stop
• .prevent
• .capture
• .self
• .once
＜ ！一阻止单击事件冒泡一〉 <a @click.stop=”handle "></a> 〈！一修饰符可以串联一〉 <a @click.stop.prevent=” handle ” ></a> 〈！一添加事件侦听器时使用事件捕获模式一〉 <p @click . capture=”handle ”> ... </p> 〈！一只当事件在该元素本身（而不是子元素） 触发时触发回调一〉 <p @click.self=” handle ”> ... </p> ＜ ！一只触发一次，组件同样适用一〉 <p @click.once=” handle ”> ... </p>
When monitoring keyboard events on a form element, also You can use key modifiers, such as calling a method only when a specific key is pressed:
＜ ！一只有在keyCode 是13 时调用vm.submit()一〉 <input @keyup.13 ＝“ submit ”〉
3. v-model: two-way binding of data; used for form input, etc.; for example: < input v-model = "message">
4. v-show: conditional rendering instruction, set the css style attribute for DOM
5. v-if: conditional rendering instruction, dynamically added in DOM Or delete DOM elements
6. v-else: conditional rendering instruction, must be used in pairs with v-if
7. v-else-if: judge multi-layer conditions, must be paired with v -if used in pairs;
8, v-text: Update the textContent of the element; for example: is equivalent to < span>{{ msg}} ;
9. v-html: Update the innerHTML of the element; the tag name will also be included.
10. v-for: loop instruction; for example:
<p id= "app ">
<ul>
<li v-for="book in books">{ { book.name } }</li>
</ul>
</p>
var app =new Vue({
el: '#app',
data: {
books: [
{name: '<vue.js实战>'},
{name: '<javascript语言精粹>'},
{name: '<javascript高级程序设计>'}
]
}
});10.1 v-for expressionSupports an optional parameter as the index of the current item when traversing the array , For example:
<p id="app">
<ul>
<li v-for="(book , index) in books ">{{ index}} - {{book.name })</li>
</ul>
</p>10.2 v-For expressionWhen traversing the object attributes, there are two optional parameters, namely key name and index:
<p id= "app">
<ul>
<li v-for="(value , key , index) in user ">
{ { index } } - { { key } } : { { value } }
</li>
</ul>
</p>
var app = new Vue({
el: '#app',
data: {
name: 'Aresn',
grender: '男',
age:23
}
});10.3 v - The expression of for can also iterate over integers:
<p id="app">
<span v-for="n in 10">{{n}}</span>
</p>10.4 Array update
When we modify the array, Vue will detect the data change, so the view rendered with v-for will also immediately renew.
• push()
• pop()
• shift()
• unshit()
• splice()
• sort()
• reverse ()
These methods will change the original array called by these methods
For example, we will add an item to the data books of the previous example:
app.books.push({
name: '《css世界》'
});Some methods will not Change the original array, for example:
• filter()
• concat()
• slice()
They return a new array. When using these non-mutation methods When Vue detects changes in the array, it does not directly re-render the entire list, but maximizes the reuse of DOM elements.
In the replaced array, items containing the same elements will not be re-rendered, so you can boldly replace the old array with a new array without worrying about performance issues.
10.5 Filtering and Sorting
当你不想改变原数组，想通过一个数组的副本来做过滤或排序的显示时， 可以使用计算属性来返回过滤或排序后的数组 ，例如：
<p id="app">
<ul>
<template v-for="book in filterBooks">
<li>书名：{{book.name}}</li>
<li>作者：{{book.author}}</li>
</template>
</ul>
</p>
var app= new Vue({
el: '#app',
computed: {
filterBooks: function(){
return this.books.filter(function (book) {
return book.name.match(/JavaScript/);
})
},
}
});11、v-cloak：不需要表达式，这个指令保持在元素上直到关联实例结束编译； v-cloak 是一个解决初始化慢导致页面闪动的最佳实践 ；
12、v-once：也是一个不需要表达式的指令，作用是定义它的元素或组件只渲染一次，包括元素或组件的所有子节点。
首次渲染后，不再随数据的变化重新渲染，将被视为静态内容； v-once 在业务中也很少使用，当你需要进一步优化性能时，可能会用到。
13、v-pre：不需要表达式，跳过这个元素以及子元素的编译过程，以此来加快整个项目的编译速度；例如： < span v-pre>{{ this will not be compiled }} </ span>；
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