angular/aio/content/guide/class-binding.md

# Class and style binding

Use class and style bindings to add and remove CSS class names from an element's `class` attribute and to set styles dynamically.

## Prerequisites

* [Property binding](guide/property-binding)

## Binding to a single CSS `class`

To create a single class binding, type the following:

`[class.sale]="onSale"`

Angular adds the class when the bound expression, `onSale` is truthy, and it removes the class when the expression is falsy—with the exception of `undefined`.  See [styling delegation](guide/style-precedence#styling-delegation) for more information.

## Binding to multiple CSS classes

To bind to multiple classes, type the following:

`[class]="classExpression"`

The expression can be one of:

* A space-delimited string of class names.
* An object with class names as the keys and truthy or falsy expressions as the values.
* An array of class names.

With the object format, Angular adds a class only if its associated value is truthy.

<div class="alert is-important">

With any object-like expression&mdash;such as `object`, `Array`, `Map`, or `Set` &mdash;the identity of the object must change for Angular to update the class list.
Updating the property without changing object identity has no effect.

</div>

If there are multiple bindings to the same class name, Angular uses [styling precedence](guide/style-precedence) to determine which binding to use.

The following table summarizes class binding syntax.

| Binding Type         | Syntax                      | Input Type                                                                  | Example Input Values |
|:---                  |:---                         |:---                                                                         |:---                  |
| Single class binding | `[class.sale]="onSale"`     | <code>boolean &verbar; undefined &verbar; null</code>                       | `true`, `false`                      |
| Multi-class binding  | `[class]="classExpression"` | `string`                                                                    | `"my-class-1 my-class-2 my-class-3"` |
| Multi-class binding  | `[class]="classExpression"` | <code>Record&lt;string, boolean &verbar; undefined &verbar; null&gt;</code> | `{foo: true, bar: false}`            |
| Multi-class binding  | `[class]="classExpression"` | <code>Array&lt;string&gt;</code>                                            | `['foo', 'bar']`                     |

## Binding to a single style

To create a single style binding, use the prefix `style` followed by a dot and the name of the CSS style.

For example, to set the `width` style, type the following:  `[style.width]="width"`

Angular sets the property to the value of the bound expression, which is usually a string. Optionally, you can add a unit extension like `em` or `%`, which requires a number type.

1. To write a style in dash-case, type the following:

    <code-example language="html">&lt;nav [style.background-color]="expression"&gt;&lt;/nav&gt;</code-example>

2. To write a style in camelCase, type the following:

    <code-example language="html">&lt;nav [style.backgroundColor]="expression"&gt;&lt;/nav&gt;</code-example>

## Binding to multiple styles

To toggle multiple styles, bind to the `[style]` attribute&mdash;for example, `[style]="styleExpression"`.  The `styleExpression` can be one of:

* A string list of styles such as `"width: 100px; height: 100px; background-color: cornflowerblue;"`.
* An object with style names as the keys and style values as the values, such as `{width: '100px', height: '100px', backgroundColor: 'cornflowerblue'}`.

Note that binding an array to `[style]` is not supported.

<div class="alert is-important">

When binding `[style]` to an object expression, the identity of the object must change for Angular to update the class list.
Updating the property without changing object identity has no effect.

</div>

### Single and multiple-style binding example

<code-example path="attribute-binding/src/app/single-and-multiple-style-binding.component.ts" header="nav-bar.component.ts"></code-example>

If there are multiple bindings to the same style attribute, Angular uses [styling precedence](guide/style-precedence) to determine which binding to use.

The following table summarizes style binding syntax.

| Binding Type                    | Syntax                      | Input Type                                                                 | Example Input Values |
|:---                             |:---                         |:---                                                                        |:---                  |
| Single style binding            | `[style.width]="width"`     | <code>string &verbar; undefined &verbar; null</code>                       | `"100px"`                           |
| Single style binding with units | `[style.width.px]="width"`  | <code>number &verbar; undefined &verbar; null</code>                       | `100`                               |
| Multi-style binding             | `[style]="styleExpression"` | `string`                                                                   | `"width: 100px; height: 100px"`     |
| Multi-style binding             | `[style]="styleExpression"` | <code>Record&lt;string, string &verbar; undefined &verbar; null&gt;</code> | `{width: '100px', height: '100px'}` |

{@a styling-precedence}
## Styling precedence

A single HTML element can have its CSS class list and style values bound to multiple sources (for example, host bindings from multiple directives).

## What’s next

* [Component styles](/guide/component-styles)
* [Introduction to Angular animations](/guide/animations)

@reviewed 2022-05-09