What should I do if the value of the vue state machine is lost?

1. Foreword

The state machine in the Vue framework is a very important part. It links data changes and view updates through getters and setters. However, in the process of using the Vue state machine, you may encounter some state loss problems. This article will analyze the causes of this problem and provide solutions.

2. Working principle of state machine

In the Vue framework, the state machine is a responsive data processing mechanism. It connects data and views through the visitor mode and the observer mode to achieve the purpose of data-driven view updates.

Specifically, the state machine in the Vue framework mainly consists of the following parts:

1. Data Object: The data of the state machine is stored in a JavaScript object .
2. Getter and Setter methods: The data reading and modification of the state machine are implemented through the Getter and Setter methods.
3. Watcher object: The Watcher object is responsible for monitoring changes in the data object. When the data changes, it will automatically trigger Vue's re-rendering process.
4. Dep object: The Dep object manages the subscription and notification mechanism of the Watcher object to ensure that they can correctly trigger Vue's re-rendering.

3. Reasons for state loss

The state machine in the Vue framework may suffer from state loss under some special circumstances. The main situations are as follows:

1. Object assignment: In the Vue state machine, data changes need to be carried out through the Setter method. However, when assigning a JavaScript object to the data object of the Vue state machine, Vue will consider this a reassignment behavior and will not automatically trigger the Setter method. As a result, the Watcher object and the Dep object cannot correctly sense data changes, and thus cannot perform correct data and view updates.
2. Array changes: Array changes in the Vue state machine require the use of mutation methods provided by Vue, such as push, pop, shift, unshift, splice, etc. However, if we use JavaScript's native array method to modify the array in the Vue state machine, it will also cause state loss. This is because if you use JavaScript's native array method to modify the array in the Vue state machine, Vue cannot sense the changes in the array, and thus cannot update the data and views correctly.
3. Multi-layer nesting of objects: In the Vue state machine, the nesting of multi-layer objects may cause the problem of state loss. This is because Vue can only correctly perceive the first-layer properties of the data object. If we need to modify multi-layer properties, we need to manually trigger the Setter method ourselves.

4. Solution

In response to the above state loss problem, we can adopt the following solutions to solve it:

1. Object assignment: If we need to To assign a JavaScript object to a data object in the Vue state machine, you can use the Vue.set or Vue.delete method provided by Vue. For example:

// 以对象name中的属性为例
Vue.set(this.obj.name, 'prop', 'value')
Vue.delete(this.obj.name, 'prop')

2. Array change: If we need to change the array in the Vue state machine, we can use the mutation methods provided by Vue (push, pop, shift, unshift, splice, etc.) . For example:

// 向数组中添加一项
this.arr.push('new item')

3. Nesting of multi-layer objects: If we need to modify multi-layer properties in the Vue state machine, we can trigger the Setter method of the parent property. For example:

// 以对象name中的属性为例
this.$set(this.obj, 'name', {
  prop: 'value'
})

In summary, we need to write code strictly in accordance with the design principles of the Vue framework to avoid the problem of state loss. If you encounter the problem of state loss during actual development, you can fix it through the above solutions.

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