Instruction function in Vue3: Custom instructions make your code more flexible

Vue is a very popular front-end framework. In the process of using Vue in recent years, we often use instructions to operate the display and hiding functions of DOM elements, such as v-if and v-show. However, with the release of Vue3, the directive function (Directive Function) has achieved major changes and improvements. A very useful directive has been added to Vue3-custom directive. This article will introduce the instruction functions in Vue3 in detail, especially the usage and advantages of custom instructions.

1. The basic concept of directive function

In Vue, directive is a special prefix attribute used in templates. The value of the instruction is expected to be a single JavaScript expression (except v-for, which will be mentioned later). The function of the instruction is to apply its associated effects to the DOM responsively when the value of the expression changes. For example, using the v-if directive in a template, you can control whether an element is displayed based on the value of an expression.

The instruction function in Vue3 is a function that can receive four parameters. It can access the element to which the instruction is bound, as well as various attributes and events on the DOM element, and can also interact with Vue components. Perform data interaction. The following are the four parameters of the instruction function:

• el: The element to which the instruction is bound can use el to obtain or modify the attributes, styles, etc. of the element.

• binding: An object containing the following properties:

  • name: The name of the directive, excluding the v- prefix.
  • value: The binding value of the directive, for example, in v-my-directive="1 1", the binding value is 2.
  • oldValue: The previous value of the instruction binding, only available in update and componentUpdated hooks.
  • expression: Instruction expression in string form. For example, v-my-directive="1 1", the value of expression is "1 1".
• vnode: The virtual node generated by Vue compilation.
• prevVNode: The previous virtual node, only available in update and componentUpdated hooks.

The instruction function accesses instruction-related information through the attributes in the binding object, and operates DOM elements through the el object.

It should be noted that the instruction function in Vue3 is only responsible for interacting with DOM elements. If data processing or business logic processing is required, other functions or methods need to be called in the instruction function to achieve it.

2. How to use custom instructions

Vue3 provides a very convenient way to customize instructions. You only need to call the Vue.directive function and pass in the instruction name and instruction function. You can customize a command. Here is a simple example:

<template>
  <div v-my-directive>Custom Directive</div>
</template>

<script>
  import { directive } from 'vue';

  const myDirective = {
    mounted(el, binding) {
      console.log('custom directive mounted', binding);
    }
  }

  export default {
    directives: {
      'my-directive': myDirective,
    },
  };
</script>

In the above example, we called the Vue.directive function and passed in the directive name 'my-directive' and the directive function myDirective. Then register the directive in the directives option of the component, and you can use the v-my-directive custom directive in the template.

The mounted hook function in the myDirective function will be called when the bound DOM element is inserted into the parent element. In this function, we can obtain the currently bound DOM element through the el parameter, obtain the binding value of the instruction and other information through the binding parameter, and perform corresponding operations.

3. Advantages of custom instructions

Compared with built-in instructions such as v-if and v-show, the advantage of custom instructions is that they can be freely expanded and customized according to business needs. The following are some advantages of custom instructions:

1. Code reusability

Custom instructions can encapsulate common code logic into one instruction, which can be repeated in multiple places. Used to reduce the workload of repetitive code writing.

2. Enhance code readability

When using built-in instructions, you need to mix logic and views together, which reduces the readability of the code, but using automatic Defining directives separates logic and views, improving code clarity and readability.

3. Enhance code maintainability

Using custom instructions, different business logic can be processed separately, thereby reducing the amount of code and enhancing the maintainability of the code. sex. When maintaining code, processing the logic of instruction binding according to different needs can greatly reduce the complexity of the code.

In short, custom instructions provide us with the possibility to freely control the view and logic, making us more flexible, convenient and efficient when writing code. It is a skill worth mastering.

4. Application scenarios of custom instructions

1. Form verification

Form verification is a common problem encountered in front-end development. Through custom instructions, we can encapsulate the verification logic into one instruction for easy use in multiple forms. For example, we can customize a v-validate directive, which will verify whether the form is legal when it is submitted.

2. Permission Control

Through custom instructions, we can easily implement the permission control function. For example, we can customize a v-auth directive that will control the display of an element based on user permissions.

3. Page scrolling

When the page is scrolling, it is often necessary to listen to the events of the scroll bar and handle them accordingly. Through custom instructions, we can easily implement the scroll control function. For example, we can customize a v-scroll directive, which will control the display and hiding of corresponding DOM elements according to page scrolling.

4. Throttling and anti-shaking

Throttling and anti-shaking are one of the ways to optimize page performance. In Vue3, throttling and anti-shake functions can also be implemented through custom instructions. For example, we can customize a v-throttle directive, which will convert frequently triggered events into triggers after a specified time interval.

5. Summary

The command function is one of the very important concepts in Vue. Through custom instructions, we can flexibly control views and logic, making the code clearer, more efficient, and easier to maintain. Compared with simple built-in instructions such as v-if and v-show, custom instructions are more powerful and suitable for various scenarios. Try using custom directives to make your code more flexible!

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