vue watchEffect
时间: 2024-03-05 16:46:49 浏览: 66
Vue的watchEffect是Vue 3中引入的一个新特性,它用于监视响应式数据的变化并执行相应的副作用函数。watchEffect函数接收一个副作用函数作为参数,并在副作用函数中访问响应式数据。当响应式数据发生变化时,副作用函数会被重新执行。
watchEffect的使用方式非常简单,只需要在组件中调用watchEffect函数,并传入一个副作用函数即可。副作用函数可以访问组件中的响应式数据,当这些数据发生变化时,副作用函数会被重新执行。
下面是一个使用watchEffect的示例:
```javascript
import { watchEffect, reactive } from 'vue';
export default {
setup() {
const state = reactive({
count: 0,
});
watchEffect(() => {
console.log('count changed:', state.count);
});
return {
state,
};
},
};
```
在上面的示例中,我们创建了一个响应式对象state,并在watchEffect中定义了一个副作用函数。当state.count发生变化时,副作用函数会被重新执行,并打印出新的count值。
相关问题
vue watcheffect
Vue's `watchEffect` is a reactive function that watches for changes in reactive properties and executes a callback function when a change occurs. It is similar to Vue's `computed` property, but instead of returning a value, it directly executes a function.
The `watchEffect` function takes in a callback function that contains the reactive properties that you want to watch. When any of these properties change, the callback function is executed. Vue automatically tracks all the reactive properties used in the callback function and only executes it when necessary.
Here's an example of using `watchEffect`:
```
<template>
<div>
<h1>Count: {{ count }}</h1>
<button @click="increment">Increment</button>
</div>
</template>
<script>
import { watchEffect, reactive } from 'vue'
export default {
setup() {
const state = reactive({
count: 0
})
const increment = () => {
state.count++
}
watchEffect(() => {
console.log(`Count has changed to ${state.count}`)
})
return {
count: state.count,
increment
}
}
}
</script>
```
In this example, we're using `watchEffect` to log a message to the console whenever the `count` property changes. We're also using Vue's `reactive` function to create a reactive state object that contains the `count` property. When the `increment` function is called, it increases the `count` property, which triggers the `watchEffect` callback function.
Note that we're returning the `count` and `increment` variables from the `setup` function so that they can be used in the template. Vue's `reactive` function and `watchEffect` are part of the Composition API, which is a new way of writing Vue components introduced in Vue 3.
vue3watchEffect
Vue 3中的`watchEffect`是一个用于监听响应式数据变化的函数。它会自动追踪其内部使用的响应式数据,并在数据变化时执行相应的回调函数。
`watchEffect`的使用方式非常简单,只需要将需要监听的代码放在一个回调函数中即可。当响应式数据发生变化时,回调函数会被自动触发执行。
下面是一个示例代码:
```javascript
import { reactive, watchEffect } from 'vue';
const state = reactive({
count: 0,
});
watchEffect(() => {
console.log('count:', state.count);
});
// 修改count的值,会触发watchEffect的回调函数
state.count++; // 输出:count: 1
state.count++; // 输出:count: 2
```
在上面的示例中,我们创建了一个响应式对象`state`,其中包含一个属性`count`。然后使用`watchEffect`来监听`state.count`的变化,并在每次变化时输出当前的值。
需要注意的是,`watchEffect`会立即执行一次回调函数,以便初始化时获取初始值。之后,只要被监听的响应式数据发生变化,回调函数就会被再次执行。
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