How to create instructions in vue

Vue.js is an extensible JavaScript framework that provides many features for building interactive web applications. One of the features for customizing and controlling DOM elements are Vue directives. This article will introduce how to create directives in Vue.js.

Overview

In Vue.js, directives are HTML attributes with a special prefix. For example, "v-" is the prefix for Vue directives. The value of a directive can be a JavaScript expression or a "directive parameter", which is the colon-separated value after the directive name. Directives can receive one or more parameters and have lifecycle hooks.

The following example demonstrates how to use directives in Vue.js:

<div></div>

Here, "v-my-directive" is the directive name, "foo" is the directive parameter, and "bar" is Instruction modifier. Instructions can also accept expressions:

<div></div>

Create instructions

To use Vue instructions, you first need to define an instruction function. The Vue instruction function can accept four parameters: el, binding, vnode and oldVnode. These parameters are the DOM element of the element bound by the instruction, the object bound by the instruction, the virtual node generated by Vue compilation and the old virtual node.

The instruction function has some hook functions, which are similar to the hook functions of the Vue component. Here are some common directive hooks:

• bind: Called only once, the first time the directive is bound to an element. Some initial settings can be made here.
• inserted: Called when the bound element is inserted into the parent node (only applicable to element nodes).
• update: Called when a component is updated, but possibly before its child components are updated.
• componentUpdated: Called after component update is completed.
• unbind: Called only once, when the instruction is unbound from the element.

The following is a simple custom directive example:

Vue.directive('my-directive', {
  bind: function (el, binding) {
    el.innerHTML = binding.value.toUpperCase();
  }
});

Here, we define a global directive using the Vue.directive functionmy- directive. This command function has a bind hook that accepts el and binding parameters. When this directive is bound to an element, el.innerHTML will be set to the uppercase version of binding.value.

Using Directives

After you define a directive, you can use it as an attribute of an HTML element. The following example demonstrates the usage of the my-directive directive:

<div></div>

Here message is a data attribute defined in the Vue instance. When a directive is bound to an element, the value of message is passed to the binding.value parameter of the directive function and processed.

You can also use a colon to specify the modifiers of the instruction:

<div></div>

In the instruction function, you can use binding.modifiers to access the modifiers of the instruction. In this example, if the directive name is my-directive and has the some-modifier modifier, binding.modifiers will return {someModifier: true} value.

Remove instructions

Sometimes you need to add or delete instructions dynamically. Vue.js provides the abbreviation : of the v-bind directive. Therefore, a directive can be removed by setting an attribute to null:

<div></div>

In this example, the directive is bound to the element if the condition condition is met, otherwise it is unbound from the element tie.

Conclusion

This article introduces the creation and use of directives in Vue.js, which can control DOM elements and the logic of interacting with them. Now you can customize your directives and enhance your Vue.js application.

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