How to use the scoped attribute of style in vue

This article mainly introduces the scoped attribute of style used with caution in Vue. The editor thinks it is quite good. Now I will share it with you and give you a reference. Let’s follow the editor and take a look.

In the vue component, in order to privatize (modularize) the style and not pollute the global situation, you can add the scoped attribute to the style tag to indicate that it only belongs to the current moment. Modules, this is a very good move, but why should it be used with caution? Because when we need to modify the style of public components (third-party libraries or project-customized components), scoped often causes more difficulties and requires additional complexity.

The principle of scoped implementation of privatized styles

Why do you think it will increase complexity? So let's start with the principles of implementing modules. For convenience of naming, we assume that this kind of component is called module private component, and other unscoped components are called module general components.

By looking at the DOM structure, we found that vue adds unique and non-repeating tags to the DOM structure and css style to ensure uniqueness and achieve the purpose of privatizing and modularizing the style. The specific rendering result is explained through an example.

Public component button component

A public component button, in order to modularize the style, add the scoped attribute to it,

//button.vue
<template>
  <p class="button-warp">
    <button class="button">text</button>
  </p>
</template>
...
<style scoped>
  .button-warp{
    display:inline-block;
  }
  .button{
    padding: 5px 10px;
    font-size: 12px;
    border-radus: 2px;
  }
</style>

Browse The browser renders the button component

The html part and css part rendered by the button component in the browser are:

<p data-v-2311c06a class="button-warp">
  <button data-v-2311c06a class="button">text</button>
</p>

.button-warp[data-v-2311c06a]{
  display:inline-block;
}
.button[data-v-2311c06a]{
  padding: 5px 10px;
  font-size: 12px;
  border-radus: 2px;
}

As can be seen from the above words, the component with the scoped attribute added , in order to achieve modularization of component styles, two processes were done:

1. Add a non-repeating data attribute (in the form: data-v-2311c06a) to the HTML DOM node to represent it Uniqueness

2. Add a data attribute selector of the current component (such as [data-v-2311c06a] at the end of each css selector (compiled and generated css statement) ) to privatize styles

Everyone knows that CSS styles have a priority. Although the operation of scoped achieves the purpose of modularizing component styles, it will cause a Consequences: The weight of each style is increased: in theory, if we want to modify this style, a higher weight is needed to cover this style. This is one of the dimensions that adds complexity.

Other components reference the button component

The above analyzes the result of a single component rendering, so what will be the result after the components call each other? , specifically divided into two situations: module general components refer to module private components (essentially the same as module private components refer to module general components); module private components refer to module private components.

For example: If the button component is used in the component content.vue, what is the difference in the rendering result whether the content.vue component adds the scoped attribute?

//content.vue
<template>
  <p class="content">
    <p class="title"></p>
    <!-- v-button假设是上面定义的组件 -->
    <v-button></v-button>
  </p>
</template>
...
<style>
  .content{
    width: 1200px;
    margin: 0 auto;
  }
  .content .button{
    border-raduis: 5px;
  }
</style>

The general components of the module (not scoped) refer to the private components of the module

If the scoped attribute is not added to the style, then the rendered html and css are:

<p class="content">
  <p class="title"></p>
  <!-- v-button假设是上面定义的组件 -->
  <p data-v-2311c06a class="button-warp">
    <button data-v-2311c06a class="button">text</button>
  </p>
</p>

/*button.vue渲染出来的css*/
.button-warp[data-v-2311c06a]{
  display:inline-block;
}
.button[data-v-2311c06a]{
  padding: 5px 10px;
  font-size: 12px;
  border-radus: 2px;
}
/*content.vue渲染出来的css*/
.content{
  width: 1200px;
  margin: 0 auto;
}
.content .button{
  border-raduis: 5px;
}

Yes It can be seen that although the border-raduis attribute of the button is modified in the content component, due to the weight relationship, the style inside the component still takes effect (at this time, the external style is overwritten). So if we want to achieve the purpose of modifying the style, we must increase the weight of the style we want to modify (increase selector level, ID selector, parallel selector, important, etc.)

Module private components (add scoped ) Reference module private components

What if the scoped attribute is added? According to the rules analyzed at the beginning (this is also true):

First add the data attribute to all DOM nodes

Then add the data attribute selector at the end of the css selector

Then the rendered html and css are:

<p data-v-57bc25a0 class="content">
  <p data-v-57bc25a0 class="title"></p>
  <!-- v-button假设是上面定义的组件 -->
  <p data-v-57bc25a0 data-v-2311c06a class="button-warp">
    <button data-v-2311c06a class="button">text</button>
  </p>
</p>

/*button.vue渲染出来的css*/
.button-warp[data-v-2311c06a]{
  display:inline-block;
}
.button[data-v-2311c06a]{
  padding: 5px 10px;
  font-size: 12px;
  border-radus: 2px;
}
/*content.vue渲染出来的css*/
.content[data-v-57bc25a0]{
  width: 1200px;
  margin: 0 auto;
}
.content .button[data-v-57bc25a0]{
  border-raduis: 5px;
}

For the above two situations, it can be clearly seen that the results after rendering are very different.

Although we have added code in content that wants to modify the style of the button component, but look carefully, since the .content .button sentence is added at the end with the scoped tag of the content component, the last sentence actually has the fundamental effect It is not on the DOM node we want, so in this case any styles we write inside the content will not affect the button.vue component, so this is embarrassing. . . .

Of course, this problem can also be solved, that is, directly adding global styles can be modified, but this will inevitably affect the components in all places; so another method is needed to add a new one in the content.vue component without The style tag of the scoped attribute means adding two styles, one for private styles and one for public styles. This is definitely a bit shit, and both solutions cannot avoid one problem: weight! ! !

//content.vue
<template>
  <p class="content">
    <p class="title"></p>
    <!-- v-button假设是上面定义的组件 -->
    <v-button></v-button>
  </p>
</template>
...
<style scoped>
  .content{
    width: 1200px;
    margin: 0 auto;
  }
</style>
<style>
  .content .button{
    border-raduis: 5px;
  }
</style>

Is this in compliance with the regulations? It seems that I didn't see that I couldn't write it like this, and it did take effect. . . But this does increase the complexity of thinking, which is a bit distressing.

Summary the rendering rules of scoped

Summary the three rendering rules of scoped

1. Add a non-duplicate to the DOM node of HTML data attribute (form: data-v-2311c06a) to express its uniqueness

2. Add a data attribute selector of the current component (such as [data-v-2311c06a]) to the end of each css selector (compiled and generated css statement) to privatize the style

3. If the component contains other components, only the data attribute of the current component will be added to the outermost tag of other components

Solution

For the referenced third-party library, if the other party uses scoped, we cannot change anything. If we really need to modify its style, we can best modify the style in the component without scoped, or globally Modifying the style directly is very rude!

For the components you maintain, you must think clearly whether the style of the component can meet all situations. If it is really necessary to add it, it will undoubtedly increase the work of the developers who use this component!

Of course, if you have a better solution to this problem, please TELL ME!

Fun facts

When using scoped, you must be careful about this feature of scoped. I thought this was a BUG, ​​so I raised an issue > ;, As a result, Youda replied very domineeringly
The original intention of scoped design is not to allow the style of the current component to modify the style of any other place, because the design is like this. So of course this issue has been closed

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

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