How to use v-on to listen for events in Vue

Vue is a popular JavaScript framework that has become a very popular choice for many developers. It uses a responsive system and componentization to allow developers to quickly create interactive front-end applications. Among them, the v-on instruction is a very useful tool, which allows developers to easily monitor various events in Vue applications. This article will introduce how to use v-on to listen for events in Vue.

1. Basic usage of v-on

The v-on command is actually an abbreviation for event binding. It can monitor DOM events, such as clicks, mouse hovers, and keyboards. Press and so on. The following is the basic usage of v-on, taking monitoring click events as an example:

<button v-on:click="handler">Click me</button>

In the above code, we use the v-on instruction to listen for click events and bind the event to a handler method. When the user clicks the button, the handler method is triggered.

You can also use the following abbreviation:

<button @click="handler">Click me</button>

This is the abbreviation of the v-on instruction, and the effect is exactly the same as the above code.

2. Processing method of listening events

Generally, we need to manually define a method in the Vue instance to handle the event. The name of the method can be customized, and we can write processing functions in the method.

<template>
  <button v-on:click="handleClick">Click me</button>
</template>

<script>
export default {
  methods: {
    handleClick: function (event) {
      // 处理点击事件
    }
  }
}
</script>

In the above code, we defined a handleClick method in the Vue component to handle click events. When the user clicks the button, this method will be triggered, and the event object event will be passed into the method as the only parameter. In the method, we can get some information about the event through the event object.

3. Pass parameters

If we need to pass additional parameters to the processing function, we can use the special syntax of the v-on instruction.

<template>
  <button v-on:click="handleClick('参数1', '参数2')">Click me</button>
</template>

<script>
export default {
  methods: {
    handleClick: function (arg1, arg2) {
      // 处理点击事件，并使用arg1和arg2
    }
  }
}
</script>

In the above code, we passed in two parameters in the instruction, and these two parameters will be passed to the arg1 and arg2 parameters in the handleClick function. Note that if we need to use dynamic parameters, we need to use square bracket syntax.

4. Modifiers

In addition to basic usage and passing parameters, the v-on directive also provides some modifiers to enhance event processing capabilities.

4.1 Preventing event bubbling

In Vue, events can bubble up along the component tree until they reach the root component. If we need to prevent the event from bubbling, we can call the stopPropagation() method of the Event object in the event handling method.

<template>
  <div v-on:click="outer">
    <div v-on:click="inner">
      Click me
    </div>
  </div>
</template>

<script>
export default {
  methods: {
    inner: function (event) {
      event.stopPropagation()
    },
    outer: function () {
      console.log('outer')
    }
  }
}
</script>

In the above code, we called the stopPropagation() method in the click event of the subcomponent, thus preventing the event from bubbling. If we do not call this method, the click event will trigger the handler functions in the child component and parent component in turn.

4.2 Prevent default behavior

In Vue, the event handling function can also call the preventDefault() method of the Event object to prevent the browser's default behavior. For example, we can prevent form submission or link redirection.

<template>
  <form v-on:submit.prevent="submit">
    ...
  </form>
  <a href="https://www.google.com" v-on:click.prevent>Google</a>
</template>

<script>
export default {
  methods: {
    submit: function () {
      // 阻止表单的提交行为
    }
  }
}
</script>

In the above code, we use the prevent modifier in the form's submission event, thereby preventing the form's default submission behavior. In the link's click event, we also use the prevent modifier to prevent the link from jumping.

4.3 Key modifier

In Vue, events can be used in conjunction with keystrokes. If we only want to trigger an event when a specific key is pressed, we can use key modifiers.

<template>
  <input v-on:keyup.enter="submit">
</template>

<script>
export default {
  methods: {
    submit: function () {
      // 处理键盘的回车事件
    }
  }
}
</script>

In the above code, we can use the .enter modifier in the keyup event so that the event handler is only triggered when the Enter key is pressed.

In summary, the v-on instruction is a very useful instruction, which can help us monitor various events very conveniently in Vue applications. When using the v-on instruction, we need to pay attention to basic usage, passing parameters, modifiers, etc., so that we can better use this instruction.

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