Vue.js custom directive method
In addition to the default core directives (v-model and v-show), Vue also allows the registration of custom directives.
Register a global directive v-focus. The function of this directive is to focus the element when the page is loaded.
<p id="app">
<p>页面载入时，input 元素自动获取焦点：</p>
<input v-focus></p><script>// 注册一个全局自定义指令 v-focusVue.directive('focus', { // 当绑定元素插入到 DOM 中。
inserted: function (el) {
// 聚焦元素
el.focus()
}
})// 创建根实例var a = new Vue({
el: '#app'})</script>You can also use the directives option in the instance to register local instructions, so that the instructions can only be used in this instance
<p id="app">
<p>页面载入时，input 元素自动获取焦点：</p>
<input v-focus></p><script>// 创建根实例new Vue({
el: '#app',
directives: { // 注册一个局部的自定义指令 v-focus
focus: { // 指令的定义
inserted: function (el) {
// 聚焦元素
el.focus()
}
}
}
})</script>The directive definition function provides several hooks Function (optional)
bind: 只调用一次，指令第一次绑定到元素时调用，用这个钩子函数可以定义一个在绑定时执行一次的初始化动作。 inserted: 被绑定元素插入父节点时调用（父节点存在即可调用，不必存在于 document 中）。 update: 被绑定元素所在的模板更新时调用，而不论绑定值是否变化。通过比较更新前后的绑定值，可以忽略不必要的模板更新（详细的钩子函数参数见下）。 componentUpdated: 被绑定元素所在模板完成一次更新周期时调用。 unbind: 只调用一次， 指令与元素解绑时调用。
Hook function parameters
钩子函数的参数有：
el: 指令所绑定的元素，可以用来直接操作DOM 。
binding: 一个对象，包含以下属性：
name: 指令名，不包括 v- 前缀。
value: 指令的绑定值， 例如： v-my-directive="1 + 1", value 的值是 2。
oldValue: 指令绑定的前一个值，仅在 update 和 componentUpdated 钩子中可用。无论值是否改变都可用。
expression: 绑定值的字符串形式。 例如 v-my-directive="1 + 1" ，
expression 的值是 "1 + 1"。
arg: 传给指令的参数。例如 v-my-directive:foo， arg 的值是 "foo"。
modifiers: 一个包含修饰符的对象。 例如： v-my-directive.foo.bar, 修饰符对象 modifiers 的值是 { foo: true, bar: true }。
vnode: Vue 编译生成的虚拟节点，查阅 VNode API 了解更多详情。
oldVnode: 上一个虚拟节点，仅在 update 和 componentUpdated 钩子中可用。The above is the detailed content of Vue.js custom directive method. For more information, please follow other related articles on the PHP Chinese website!
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