Using custom instructions to implement special functions in Vue

Use custom instructions in Vue to implement special functions

Introduction:
Vue is a very powerful JavaScript framework that provides us with A convenient and efficient way to build interactive web applications. In addition to the built-in directives (such as v-model, v-if, etc.), Vue also allows us to create custom directives to extend its functionality.

This article will introduce how to use custom instructions in Vue to implement some special functions, and provide corresponding code examples for reference.

1. Custom global directives
Global directives can be used in any Vue component. The following is an example that demonstrates how to create a global directive to set the focus of the input box:

Vue.directive('focus', {
  inserted: function (el) {
    el.focus();
  }
});

The above code creates a directive named "focus" and defines its inserted hook function, which will be called when the bound element is inserted into the DOM. In this example, we automatically set focus on the bound element (i.e. input element) when it is inserted into the DOM.

Using global directives in Vue components is very simple, just add the v-focus directive on the corresponding element:

<input v-focus>

In this way, no matter which Vue component uses v-focus Instructions and their corresponding input boxes will automatically gain focus.

2. Custom local directives
In addition to global directives, Vue also allows us to create local directives, which means that specified directives are only available in specific Vue components. The following is an example that demonstrates how to create a local directive to limit the input box to only numbers:

Vue.component('custom-input', {
  template: `<input v-only-number>`,
  directives: {
    'only-number': {
      bind: function (el) {
        el.addEventListener('input', function (e) {
          if (!/^d*$/.test(e.target.value)) {
            e.target.value = e.target.value.replace(/[^d]/g, '');
          }
        });
      }
    }
  }
});

The above code creates a local directive named "only-number" and places it in the Vue component Used in "custom-input". This instruction binds the input event of the input box element, and when the event is triggered, it uses a regular expression to determine whether the input value is a number, and if not, replaces the non-numeric characters with an empty string.

In the Vue component that uses this custom directive, just use it as follows:

<custom-input></custom-input>

In this way, the corresponding input box can only enter numbers, and any non-numeric characters will is automatically deleted.

3. Hook functions of custom instructions
In addition to inserted and bind, Vue also provides some other hook functions to control the behavior of custom instructions in the life cycle of the component. Here are some commonly used hook functions:

• bind: Called when the directive is bound to the element, only called once.
• inserted: Called when the bound element is inserted into the DOM.
• update: Called when the component's VNode is updated, but may be called before the child component's VNode is updated.
• componentUpdated: Called after the component's VNode and the VNode of its subcomponents are updated.
• unbind: Called when the instruction is unbound from the element.

Summary:
Through custom instructions, we can easily extend the functions of Vue to meet some special needs. This article explains how to create global and local directives and provides corresponding code examples. In addition, Vue also provides a wealth of hook functions, which can provide fine control over custom instructions at different life cycle stages.

I hope this article can help you understand the use of custom instructions in Vue, and inspire you to apply them in actual projects. If there are any shortcomings, please correct me, thank you!

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