How vue mutates

Vue is a popular JavaScript framework that uses a responsive data binding mechanism to make it easier for developers to build interactive web applications. Among them, mutation is a core mechanism of Vue, which can track data changes and update the view when needed. So, how does Vue mutate? This article will explore Vue's mutation mechanism from aspects such as Vue's data change detection mechanism, mutation execution process, and mutation optimization, to help readers better understand the internal working principles of Vue.

Vue's data change detection mechanism

Vue uses a responsive data binding mechanism. Through this mechanism, Vue can track data changes and automatically update views. In Vue, data change detection is achieved by hijacking data attributes. Specifically, when Vue is initialized, it will traverse the data object and use the Object.defineProperty() method to add a getter and setter method for each property, so that when the property is accessed or assigned, the getter or setter will be triggered. method. In the setter method, Vue will register a Watcher object and add the view that needs to be updated to the dependency list of the Watcher object. When this property is assigned a value, the Watcher object is notified and the data-binding expression in the view is re-evaluated. In this way, Vue can ensure that data and views are always synchronized.

Execution process of mutation

When a property in a Vue instance is assigned a value, Vue will detect whether the property has been registered as a reactive property. If it is registered, the setter method will be triggered, and the view that needs to be updated will be added to the dependency list of the Watcher object corresponding to the property. During the next update, the Watcher object will be notified and the data-binding expressions in the view will be re-evaluated.

Specifically, Vue's mutation execution process can be divided into the following steps:

1. Data update triggers mutation: When a property in a Vue instance is assigned a value, Vue will Checks whether this property has been registered as a reactive property. If it has been registered, the setter method will be triggered and the view that needs to be updated will be added to the dependency list of the Watcher object corresponding to the property. Otherwise, the assignment operation will not trigger mutation.
2. Construction of update queue: When multiple attributes are assigned values, multiple mutation operations may be triggered, causing the view to be updated multiple times. To solve this problem, Vue uses a queue to cache Watcher objects that need to be updated. When a Watcher object is added to the update queue, if the Watcher object already exists in the queue, it will be moved to the end of the queue, otherwise the Watcher object will be added to the end of the queue.
3. Execution of mutation: When the view needs to be updated, Vue will sequentially take out the Watcher objects from the update queue and execute its corresponding update function. At the same time, when executing the update function, Vue will deduplicate and sort the dependency list of the Watcher object to ensure that each Watcher object is only processed once and updated in the order of calculated properties and component updates.

Optimization of mutation

Vue has done a lot of optimization on the mutation mechanism to improve performance and reduce useless mutation operations. Among them, there are mainly the following methods:

1. Batch update: When multiple properties are assigned values, Vue will put these operations into a microtask for execution to reduce the number of mutations. At the same time, Vue also uses a transaction-like mechanism. If multiple mutation operations occur within the same event loop cycle, Vue will only perform an update operation once.
2. Component-level updates: Vue uses virtual DOM to optimize component-level updates, that is, only update the components that need to be updated and their sub-components, rather than the entire page. In addition, Vue also uses the Diff algorithm to compare the differences between two virtual DOM trees and update only the changed parts.
3. Lazy update: When a property inside a component is updated, Vue will not perform the update operation immediately, but will wait until the parent component of the component is updated before making another update. This approach can reduce useless mutation operations and improve performance.
4. Static node optimization: Vue optimizes static nodes, that is, caches nodes that will never change, and directly reuses the results of the node in the next mutation operation. This can reduce DOM operations and improve rendering performance.

Summary

This article explores the mutation mechanism of Vue from the aspects of Vue's data change detection mechanism, mutation execution process, and mutation optimization. Mutation is a core mechanism within Vue, and its optimization is one of the important means to improve Vue performance. Understanding Vue's mutation mechanism can help developers better use Vue to build interactive web applications, and better understand the inner workings of Vue.

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