What are the differences between v-if and v-show

The differences between v-if and v-show include rendering method, performance impact, behavioral differences and usage scenarios. Detailed introduction: 1. Rendering method, the v-if instruction will conditionally render elements based on the true or false expression. When the expression is true, the element will be rendered, and the element will not be rendered. v-if has "laziness" "Feature, that is, the element will be created and inserted into the DOM only when the condition is met for the first time. The v-show directive will also conditionally render the element based on the true or false expression. Regardless of whether the expression is true or false, the element will always be will be created and inserted into the DOM etc.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

The difference between v-if and v-show is very important in Vue.js. Both directives can be used to conditionally render elements, but there are significant differences in how they render, their performance impact, and their behavior. Below I will elaborate on these differences from the following aspects:

Rendering method:

v-if: The v-if directive will conditionally render elements based on the true or false expression. When the expression is true, the element will be rendered; otherwise, the element will not be rendered. Therefore, v-if has the "lazy" property that the element will only be created and inserted into the DOM when the condition is met for the first time.

v-show: The v-show directive also renders elements conditionally based on the truth or falsehood of an expression. However, regardless of whether the expression is true or false, the element is always created and inserted into the DOM. When the expression is false, the element will not be displayed, but it will still exist in the DOM and take up space. Therefore, v-show has the characteristics of "lazy" and "always present".

Performance impact:

v-if: Since v-if dynamically creates and destroys elements based on conditions, it may have a greater impact on performance. When conditions need to be switched frequently, using v-if may cause page performance to degrade.

v-show: Since v-show does not destroy the element but simply switches the element's visibility, it has a relatively small impact on performance. Even if conditions are frequently switched, v-show will not have a significant impact on performance.

Behavior differences:

Both v-if and v-show support asynchronous operations, that is, the conditions may not change immediately. In this case, v-if will ensure that the element is rendered correctly when the condition is met; v-show may not update the element's visibility immediately.

v-if has "instant" properties when conditions change, because it destroys or recreates the element immediately. In contrast, v-show has a "gradual transition" property in that it only changes the visibility of the element.

Usage scenarios:

When you need to dynamically display or hide elements based on conditions, both v-if and v-show can be used. However, based on the above differences, we should choose the appropriate instructions according to the specific scenario. If conditions are likely to change frequently, or elements are expensive to create and destroy, v-show is usually a better choice. If the probability of the condition changing is low, and the overhead of element creation and destruction is small, then v-if may be more appropriate.

Another consideration is the purpose of the element. If the element is only for display and does not participate in interaction (for example, displaying a message or status), then v-show may be more appropriate. If the element requires user interaction (for example, form input), then using v-if ensures that the element is always available when the condition is met.

Note:

Both v-if and v-show can accept an optional parameter to specify the style of the element when the condition is false. For example, v-show="isVisible: false" will hide the element and apply the specified style when isVisible is false.

v-if does not support the CSS display: none attribute because this attribute cannot be applied after the element is destroyed. If you need to hide an element and preserve space, you can use v-show or use the CSS visibility: hidden property.

Both v-if and v-show can be used with v-else and v-else-if to implement more complex conditional rendering logic.

In short, although v-if and v-show can both implement conditional rendering, they have significant differences in rendering methods, performance impact, and behavior. Therefore, in practical applications, we need to choose appropriate instructions according to specific needs.

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