How to use watch in vue

The watch option in Vue.js allows developers to listen for changes in specific data. When the data changes, watch triggers a callback function to perform update views or other tasks. Its configuration options include immediate, which specifies whether to execute a callback immediately, and deep, which specifies whether to recursively listen to changes to objects or arrays.

Use watch in Vue.js

In Vue.js, watch option allows developers to listen for changes in specific data. Once the data changes, watch triggers a callback function that can perform tasks such as updating the view or performing other operations.

Use syntax

 <code class="javascript">watch: { // 要监听的数据属性propertyName: { // 回调函数handler(newValue, oldValue) { // 在数据发生更改时运行的代码}, // 可选：配置项immediate: true | false, // 立即执行回调deep: true | false // 深度监听对象或数组} }</code>

Example of usage

 <code class="javascript">export default { data() { return { count: 0 } }, watch: { // 监听count 属性count: { handler(newValue, oldValue) { console.log(`count 发生变化：${oldValue} -> ${newValue}`) }, // 立即执行回调immediate: true } } }</code>

In this example, count property is listened to. When count changes, the handler function will be called, which will record the change in count value. Since immediate is set to true , the callback function is executed immediately when the component is first rendered.

Configuration Options

watch option provides several configuration options for customizing its behavior:

• immediate: Specifies whether to execute the callback function immediately upon component initialization.
• deep: Specifies whether to recursively listen to changes to objects or arrays. If set to true , changes in nested properties in the array or object also trigger the callback function.

Notice:

• Avoid resetting the same data attribute in the watch callback function, which can lead to an infinite loop.
• If the objects or arrays you are listening on are large, consider using the deep option to avoid performance issues.
• If you only care about the initial value, you can use the created hook function.

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