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Class and Style Bindings

A common need for data binding is manipulating an element’s class list and its inline styles. Since they are both attributes, we can use v-bind to handle them: we just need to calculate a final string with our expressions. However, meddling with string concatenation is annoying and error-prone. For this reason, Vue.js provides special enhancements when v-bind is used for class and style. In addition to Strings, the expressions can also evaluate to Objects or Arrays.

Binding HTML Classes

Although you can use mustache interpolations such as class="{{ className }}" to bind the class, it is not recommended to mix that style with v-bind:class. Use one or the other!

Object Syntax

We can pass an Object to v-bind:class to dynamically toggle classes. Note the v-bind:class directive can co-exist with the plain class attribute:

<div class="static" v-bind:class="{ 'class-a': isA, 'class-b': isB }"></div>
data: {
  isA: true,
  isB: false
}

Which will render:

<div class="static class-a"></div>

When isA and isB changes, the class list will be updated accordingly. For example, if isB becomes true, the class list will become "static class-a class-b".

And you can directly bind to an object in data as well:

<div v-bind:class="classObject"></div>
data: {
  classObject: {
    'class-a': true,
    'class-b': false
  }
}

This will render the same result. As you may have noticed, we can also bind to a computed property that returns an Object. This is a common and powerful pattern.

Array Syntax

We can pass an Array to v-bind:class to apply a list of classes:

<div v-bind:class="[classA, classB]">
data: {
  classA: 'class-a',
  classB: 'class-b'
}

Which will render:

<div class="class-a class-b"></div>

If you would like to also toggle a class in the list conditionally, you can do it with a ternary expression:

<div v-bind:class="[classA, isB ? classB : '']">

This will always apply classA, but will only apply classB when isB is true.

However, this can be a bit verbose if you have multiple conditional classes. In version 1.0.19+, it’s also possible to use the Object syntax inside Array syntax:

<div v-bind:class="[classA, { classB: isB, classC: isC }]">

Binding Inline Styles

Object Syntax

The Object syntax for v-bind:style is pretty straightforward - it looks almost like CSS, except it’s a JavaScript object. You can use either camelCase or kebab-case for the CSS property names:

<div v-bind:style="{ color: activeColor, fontSize: fontSize + 'px' }"></div>
data: {
  activeColor: 'red',
  fontSize: 30
}

It is often a good idea to bind to a style object directly so that the template is cleaner:

<div v-bind:style="styleObject"></div>
data: {
  styleObject: {
    color: 'red',
    fontSize: '13px'
  }
}

Again, the Object syntax is often used in conjunction with computed properties that return Objects.

Array Syntax

The Array syntax for v-bind:style allows you to apply multiple style objects to the same element:

<div v-bind:style="[styleObjectA, styleObjectB]">

Auto-prefixing

When you use a CSS property that requires vendor prefixes in v-bind:style, for example transform, Vue.js will automatically detect and add appropriate prefixes to the applied styles.

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Licensed under the MIT License.
https://v1.vuejs.org/guide/class-and-style.html