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: { // 要監(jiān)聽的數(shù)據(jù)屬性propertyName: { // 回調(diào)函數(shù)handler(newValue, oldValue) { // 在數(shù)據(jù)發(fā)生更改時(shí)運(yùn)行的代碼}, // 可選：配置項(xiàng)immediate: true | false, // 立即執(zhí)行回調(diào)deep: true | false // 深度監(jiān)聽對象或數(shù)組} }</code>
Example of usage
<code class="javascript">export default { data() { return { count: 0 } }, watch: { // 監(jiān)聽count 屬性count: { handler(newValue, oldValue) { console.log(`count 發(fā)生變化：${oldValue} -> ${newValue}`) }, // 立即執(zhí)行回調(diào)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
watchcallback function, which can lead to an infinite loop. - If the objects or arrays you are listening on are large, consider using the
deepoption to avoid performance issues. - If you only care about the initial value, you can use the
createdhook function.
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