How vue implements display and hiding of elements (compare v-if and v-show)

Vue.js is a progressive framework for creating user interfaces. There are many advanced features in Vue, one of which is showing and hiding elements. The implementation principle of this function is actually very simple, but many Vue beginners may be confused. This article will introduce in detail how to display and hide elements in Vue.

1. v-if directive

The most basic way to display and hide elements in Vue is to use the v-if directive. The v-if directive requires adding a condition to the element to be hidden or displayed. The element will be displayed only when the condition is true, otherwise it will be hidden. For example:

<div v-if="show">这是一个需要显示或隐藏的元素</div>

In the above example, we defined a variable named show. This div element will be displayed only when the value of show is true. If the value of show is false, this element will be hidden.

2. v-show directive

In addition to the v-if directive, Vue also has a directive for showing and hiding elements, which is the v-show directive. Unlike the v-if directive, v-show does not remove the element from the DOM, but sets the element's CSS property display to none, so that the element will not be displayed on the page.

For example:

<div v-show="show">这是一个需要显示或隐藏的元素</div>

In the above example, if the value of show is true, the div element will be displayed on the page, and the value of display is set to block; if the value of show If the value is false, the div element will not be displayed on the page, and the value of display is none.

It should be noted that when we use the v-show directive, the element is still located in the DOM. This means that it still takes up space on the page. So if you need to remove it completely on the page, you should use the v-if directive.

3. Compare v-if and v-show instructions

The implementation principles of v-if and v-show instructions have been briefly introduced above. But when we need to add show or hide functionality to an element, which directive should we choose?

First of all, if you need to conditionally hide or show certain elements when the document is loaded, you should use the v-if directive. This is because the v-if directive removes the element from the DOM, so it doesn't take up page space like the v-show directive does. Therefore, if you need to add some complex initialization logic when the page loads, using the v-if directive is a good choice.

Secondly, if you need to show and hide an element multiple times, you should use the v-show directive. This is because using the v-show directive can avoid repeatedly recreating and destroying elements, which will cause the page to be redrawn and affect performance.

Finally, when we need to make conditional judgments when using v-if or v-show, we should use the logical expressions of these two instructions to make conditional judgments. In this way, we can use them flexibly in our code and write more flexible and powerful Vue applications.

Summary:

It is very simple to display and hide elements in Vue. We just need to use the v-if or v-show directive to achieve this. If you need to hide or show certain elements while the document is loading, you should use the v-if directive. If you need to show and hide an element multiple times, you should use the v-show directive. When using these two instructions, we should use the logical expressions of these two instructions for conditional judgment, so that we can use them flexibly in the code and write more flexible and powerful Vue applications.

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