Let’s talk about how to use vue custom instructions

Vue is a popular JavaScript framework that can help us build interactive web applications. Vue provides many powerful functions and features, one of the important features is directives. Directives are a custom HTML attribute provided by Vue that allow us to write more complex behaviors in templates. This article will introduce how to implement Vue custom instructions.

1. Basic syntax

The Vue command is a custom HTML attribute. The syntax format is v-command name. You can add a colon (:) and parameters after the command name, for example:

<!-- v-my-directive -->
<!-- v-my-directive:param -->

Instructions can have hook functions such as bind, update, inserted, componentUpdated and unbind. These hook functions allow us to execute custom code at different points in the instruction life cycle. For example, perform a certain operation when binding instructions:

Vue.directive('my-directive', {
  bind: function(el, binding, vnode) {},
  update: function(el, binding, vnode, oldVnode) {},
  inserted: function(el, binding, vnode) {},
  componentUpdated: function(el, binding, vnode, oldVnode) {},
  unbind: function(el, binding, vnode) {}
})

2. Implement simple instructions

First, let’s look at a simple custom instruction, which can change the background color of an element Set to red. The code is as follows:

Vue.directive('red-bg', {
  bind: function(el, binding, vnode) {
    el.style.backgroundColor = 'red';
  }
})

In this example, we set the background color of the element to red in the bind hook function. Now, we can use this custom directive in our template:

<div v-red-bg></div>

When the page loads, the background color of this element will be automatically set to red.

3. Instruction parameters

Now, let’s take a look at how to implement a custom instruction with parameters. Adding parameters to the directive allows us to pass some additional data in the template. For example, we can define a custom directive that converts the text content of an element to uppercase letters. The code is as follows:

Vue.directive('uppercase', {
  bind: function(el, binding, vnode) {
    el.textContent = binding.value.toUpperCase();
  }
})

In this example, we use the directive hook function bind. In this hook function, we convert the value of binding.value (the directive parameter) to uppercase letters and set it as the text content of the element. Now, we can use this custom directive in the template and pass the parameters:

<div v-uppercase="text"></div>

In this example, we use the v-uppercase directive and set the directive parameter to text. After the page loads, the text content of the element will be automatically converted to uppercase letters.

4. Instruction Modifiers

Instruction modifiers are a simple but powerful technology provided by Vue to extend the behavior of instructions. Directive modifiers are special tags starting with ".", such as v-my-directive.foo and v-my-directive.bar. Modifiers can modify the behavior of a directive, such as disabling default behavior or changing the events the directive responds to. Here is an example of using directive modifiers:

Vue.directive('my-directive', {
  bind: function(el, binding, vnode) {
    el.addEventListener('click', function() {
      // 阻止事件冒泡
      if (binding.modifiers.stop) {
        event.stopPropagation();
      }

      // 阻止默认行为
      if (binding.modifiers.prevent) {
        event.preventDefault();
      }
    })
  }
})

In this example, we use the v-my-directive directive and add two modifiers stop and prevent. In the bind hook function, we added a click event listener and prevented event bubbling and default behavior based on the value of the modifier. Now, we can use this custom directive in the template and add the modifiers:

<div v-my-directive.stop.prevent></div>

In this example, we used the v-my-directive directive and added the two modifiers stop and prevent. When the user clicks on this element, the event will be prevented from bubbling and default behavior.

5. Summary

Custom instructions are a powerful feature provided by Vue, which allows us to extend the behavior of templates. Custom directives can receive parameters and modifiers and execute custom code in hook functions. By learning how to implement custom directives, we can better take advantage of Vue's capabilities and add more interactivity and complexity to our web applications.

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