How to solve the problem that vue does not update the array subscript view when changing it

Vue is a popular front-end framework that allows developers to easily build single-page applications. Although Vue is extremely flexible and powerful, sometimes encountering unexpected problems can confuse developers.

A very common Vue problem occurs when the array index is changed, but the view is not updated, even if the v-for directive is used. Below we’ll dive into why this problem occurs and how to fix it.

Vue’s responsive system

In Vue, data changes drive view updates. When the application starts, Vue extracts each property from the data object and converts it into a getter/setter. When the data changes, the setter will notify Vue to update the view. This is the core principle of Vue’s reactive system.

For arrays, Vue will process operations that modify its length and use methods such as splice(), push() and pop() to ensure that the view can respond correctly. However, if the array index is modified, Vue will not be able to detect this change.

The root of the problem is that Vue's reactive system cannot detect changes in array subscripts. Specifically, this is because when the array subscript is modified, the data inside the array does not change. Vue's reactive system updates the view only by manipulating the elements in the array.

Solution 1: Use $set

Vue provides the $set() method, which allows us to modify the elements in the array and notify Vue's reactive system to update the view. The $set() method receives three parameters: the array, the index of the element to be modified, and the new value.

this.$set(this.myArray, index, newValue);

At this time, Vue will sense the changes in the elements in the array and will update the view. Therefore, when modifying the array subscript, we should use the $set() method to modify the array elements in order to trigger the reactive system.

Solution 2: Use splice

In addition to using $set(), we can also use the splice() method to update the array and make the reactive system update the view. splice() accepts three parameters: the number of elements to remove, the number of elements to insert, and the elements to insert.

this.myArray.splice(index, 1, newValue);

When we use the splice() method, Vue will recognize the change of elements in the array and update the view.

Summary

In Vue, modifying the array subscript may cause the view to not update. However, this problem can be solved by using the $set() or splice() methods.

It should be noted that when the array is very large, using $set() or splice() at each position that changes the array index may affect performance. In this case, we can consider using reactive() and ref() provided in Vue3.x to implement responsive arrays. These APIs provide better performance and the ability to change the size and shape of the array after it is created.

Finally, understanding Vue’s reactive system is an important step in developing high-quality Vue applications. By following best practices and leveraging the power of Vue, we can create a better user experience.

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