vue watch execution process

Vue.js is a popular front-end framework that provides a processing mechanism for data changes. Vue provides a watch feature that can be used to monitor changes in data in Vue instances and perform corresponding operations when changes occur. This article will introduce the execution process of Vue watch.

1. Create a Vue instance

First, you need to create a Vue instance. Vue's data response mechanism is implemented by hijacking the accessor function of the object. When a property in a Vue instance is accessed, the property's getter function is triggered. When the property is modified, the property's setter function is triggered. Vue uses the Object.defineProperty() method to implement object hijacking.

2. Set the watch attribute

In a Vue instance, you can set a listener for a certain property through the watch attribute. When this property changes, the listener will be automatically executed. . The value of the watch attribute is an object. The attribute of the object is the name of the monitored attribute. The value of the attribute is a callback function, and corresponding operations can be performed in the callback function.

3. Execution of watch

When the monitored property changes, the watch listener will be triggered. Before executing the listener, Vue will check whether the listener has already been executed. If it has been executed, the listener will be skipped. If the listener has been executed before but is forced to be executed again, the listener will be marked as not executed before the listener is executed.

4. watch Execution of the callback function

Once the listener is called, the callback function will start executing. In the callback function, the value of this points to the Vue instance. The first parameter of the callback function is the value after the attribute changes, and the second parameter is the value before the attribute changes. In the callback function, you can access other properties in the Vue instance through this.

5. Ordering of the listener queue

When the watch attribute has multiple listeners in the component, the order in which the listeners are executed will affect the final result. In order to ensure the execution order of listeners, Vue sorts the listener queue through topological sorting. Using a topological sorting algorithm ensures that all listeners are executed in the correct order.

Summary

Vue’s watch feature can easily implement monitoring of data changes and corresponding operations. The execution process of watch includes creating Vue instance, setting watch attribute, execution of watch, execution of watch callback function and sorting of listener queue. Mastering the execution process of Vue watch can help developers better understand Vue's responsive mechanism and improve the readability and maintainability of the code.

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