The difference between id and class in vue

Vue.js is a popular JavaScript front-end framework that uses powerful data binding and component-based architecture to build modern web applications. Vue.js draws on the advantages of Angular and React, but also has its own unique features.

In the Vue.js template, you can use the id and class selectors to select elements. In CSS, id and class are identifiers used to add styles to HTML elements. However, in Vue.js, id and class have other uses. This article will explore the difference between id and class in Vue.js in detail and provide developers with useful programming tips.

1. Different uses

In HTML, id and class are usually used to represent page styles. In Vue.js, id and class not only represent styles, but are also used to manipulate DOM elements.

• id: The element id in the Vue.js component template is generally used to uniquely identify elements within a component, as shown below:

<div id="app">
  <p id="title">Hello Vue!</p>
</div>

Can be used in components Access this element through the $refs object:

export default {
  mounted() {
    console.log(this.$refs.title);
  },
}

• class: The class in the Vue.js component template can be used to select multiple elements, as shown below:

<div id="app">
  <p class="title">Hello Vue!</p>
  <p class="title">Hello World!</p>
</div>

You can use the document.getElementsByClassName method in the component to obtain these elements:

export default {
  mounted() {
    console.log(document.getElementsByClassName('title'));
  },
}

2. Different execution efficiency

The execution efficiency of id and class in Vue.js is different , mainly depends on the use case.

• id: The id is unique in the page, so getting the element through getElementById() is very fast. For Vue.js components, this element can be accessed through $refs and is very fast.
• class: Since class may be applied to multiple elements, the getElementsByClassName() method may need to iterate a large number of elements, and the execution efficiency is relatively low.

3. Different scopes

The scopes of id and class in Vue.js are different.

• id: only valid inside the component, will not affect the global
• class: not only valid inside the component, can also affect the global (unless scoped CSS is used)

This is important for CSS styling in Vue.js components. Because class names can be reused within multiple components, they are prone to conflicts globally. Vue.js can solve this problem by using the scoped attribute of CSS to make the style only apply to the current component.

<style scoped>
.title {
  color: red;
}
</style>

The CSS styles in the above code will only take effect within the current component.

Summary

• The usage and scope of id and class in Vue.js are different from those in HTML and CSS.
• In Vue.js, id and class not only represent styles, but are also used to operate DOM elements.
• The execution efficiency of id and class in components will also vary, mainly depending on the use case.
• Using the scoped feature of CSS, you can limit the style to the current component.

Understanding the functions and differences of id and class in Vue.js can allow developers to use them better and avoid unnecessary errors. Of course, with the scoped feature of CSS, most of these problems can be easily solved. Vue.js inherits the excellent ideas and technologies of modern web development frameworks, and we should be good at using them to build better applications.

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