Vue responsive data does not respond

When developing with Vue.js, the most commonly used feature is its responsive data binding. This feature allows developers to achieve automatic synchronization between views and data by declaring and binding data. But sometimes, we may encounter a problem where Vue's responsive data does not respond, that is to say, we modify the data, but the view is not updated. This is a common problem. Next, let’s discuss the possible causes and solutions to this problem.

1. The data type does not support reactive

Vue.js can only detect properties that exist when the data is initialized. Therefore, if there are some non-responsive data types, such as Map, Set, Symbol and other types of objects passed in as props of this component or parent component, then there is no way for these data types to trigger responsive updates. In this case, the update needs to be triggered manually. Use the Vue.set or Vm.$set method to manually set a new response property, for example:

Vue.set(this.obj, 'propertyName', newValue)

or

this.$set(this.obj, 'propertyName', newValue)

2. Vue is not used when adding new properties/elements to an object or array .set or this.$set

We know that when developing with Vue.js, we usually use the Object.defineProperty method to listen for data changes, so that the view can be re-rendered when the properties change. . There will be problems with the addition of new properties or elements to objects or arrays, because Vue.js cannot automatically track their changes. Therefore, if we add a new attribute to an object or add a new element to an array, we need to use the Vue.set or this.$set method to manually add the attribute or element.

For example, we have an array named data and need to add a new element:

this.data.push(newElement); // 这种方式添加的元素不会响应式更新
或者
this.data[this.data.length] = newElement; // 该方式同样不会响应式更新

The correct way is to use this.$set or Vue.set:

this.$set(this.data, this.data.length, newElement);
或者
Vue.set(this.data, this.data.length, newElement);

Similarly, adding new properties to objects is the same.

3. The object or array uses the Object.freeze() method

If the object or array is frozen by the Object.freeze() method, Vue.js cannot change it Binding properties. So, if you need to change these properties, you need to manually unfreeze and add properties/elements, for example:

let obj = Object.freeze( {
  key: 'value'
});
let newValue = 'new value';
obj.key = newValue; // 这种方式添加的属性不会响应式更新

let newObj = {[...obj]} // 这样也不会响应式更新

let unfrozenObj = {...obj}; // 解冻后再添加属性才会触发更新
unfrozenObj.key = newValue;

4. Frequently switching properties on the same object

When on the same object When attributes are frequently switched, Vue.js may fail to respond. For example, when switching a bool type attribute, you should first manually set the value of the attribute to false, and then set it to true, such as:

this.boolAttr = false;
this.boolAttr = true;

5. Number of nesting levels of objects or arrays Too deep

In Vue.js, the maximum responsiveness depth is 10 levels. If the number of nested layers of an object or array is too deep, Vue.js will not be able to track its internal property changes. . At this time, we can consider using calculated properties and methods to solve this problem. For example:

data: {
  deepChild: {
    deepChild1: {
      ...
    }
  }
},

computed: {
  deepChildProp: function() {
    return this.deepChild.deepChild1....;
  }
},

In summary, the above are several situations where Vue responsive data does not respond. When we deal with similar problems, we need to determine the cause of the problem in advance and then choose the corresponding solution. We can use the tools provided by Vue.js to diagnose ongoing problems, or manually implement unexpected updates or manipulate data in computed properties and methods. When using Vue.js, we need to fully understand its responsive data binding principles in order to write beautiful and efficient code.

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