What does watch in vue mean

watch is a responsive feature that allows you to listen to and react to changes in data properties in Vue.js, thereby automatically tracking data changes and keeping data and views in sync. The key of the watch object is the attribute to be monitored, and the value is the function to be executed when the property is changed. This function will receive new and old values ​​as parameters.

What is watch in Vue.js?

Watch in Vue.js is a responsive feature that allows you to listen to changes in data properties and react to them. When the value of the monitored property changes, the watch expression will be re-execute, thus running the associated function or performing the specified action.

How to use watch?

To use watch, you need to provide a watch object in the component's options object:

 <code class="javascript">export default { watch: { // 监视的属性及其关联函数} }</code>

The key of the watch object is the property to be monitored, and the value is the function to be executed when the property changes. This function will receive two parameters:

• newValue: the new value of the attribute
• oldValue: The old value of the attribute

Benefits of watch

Using watch can bring many benefits, including:

• Automatically track data changes without manual inspection
• Respond to changes in UI status to keep data and views synchronized
• Implement reusable, responsive components
• Conveniently handle asynchronous operations

Example

The following example shows how to use watch to listen for changes in count property and print a message after it is updated:

 <code class="javascript">export default { watch: { count: { handler(newValue, oldValue) { console.log(`count changed from ${oldValue} to ${newValue}`) } } } }</code>

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