Animate state and style link

You can define a set of styles together to make up a specific state for animating elements and transitions. These states represent style at certain points in your animations that you can animate to and from. For example, you can animate a state as the starting point to a different state and the end of an animation.

What is a state? link

A state is the condition of an animation. The Angular state() function takes two parameters: a unique name and a style. There is also an optional parameter.

Why would you want to use state? link

Aliasing a set of styles and allows you to reference that alias for animations in general. This can make animations more readable or more understandable at a glance. You can give animations a useful and descriptive state name, which allows you to quickly understand the purpose of that animation state.

Use Angular's state() function to define different states to call at the end of each transition. This function takes two arguments: A unique name like open or closed and a style() function.

Use the style() function to define a set of styles to associate with a given state name. You must use camelCase for style attributes that contain dashes, such as backgroundColor or wrap them in quotes, such as 'background-color' .

Angular's state() function works with the style⁣­(⁠) function to set CSS style attributes. In this code snippet, multiple style attributes are set at the same time for the state. In the open state, the button has a height of 200 pixels, an opacity of 1, and a yellow background color.

      
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      // ...
state('open', style({
  height: '200px',
  opacity: 1,
  backgroundColor: 'yellow'
})),
    

In the following closed state, the button has a height of 100 pixels, an opacity of 0.8, and a background color of blue.

      
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      state('closed', style({
  height: '100px',
  opacity: 0.8,
  backgroundColor: 'blue'
})),
    

Animation API summary link

The functional API provided by the @angular/animations module provides a domain-specific language (DSL) for creating and controlling animations in Angular applications. See the API reference for a complete listing and syntax details of the core functions and related data structures.

Animation transition and timing link

An animation transition specifies changes that occur between one state and another. Set the transition to make the change less abrupt. An animation transition specifies the changes that occur between one state and another.

Animation transition() function defined link

The transition() function accepts two arguments:

An expression that defines the direction between two transition states An expression that accepts one or a series of animate() steps

Use the animate() function of a transition to define:

• Length
• Delay
• Easing
• Style function for defining styles while transitions are taking place

Use the animate() function to define the keyframes() function for multi-step animations. These definitions are placed in the second argument of the animate() function.

Animation metadata: duration, delay, and easing link

The animate() function accepts the timings and styles input parameters.

The timings parameter takes either a number or a string defined in three parts.

      
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      animate (duration)
    

or

      
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      animate ('duration delay easing')
    

The first part, duration , is required. The duration can be expressed in milliseconds as a number without quotes, or in seconds with quotes and a time specifier. For example, a duration of a tenth of a second can be expressed as follows:

• As a plain number, in milliseconds: 100

• In a string, as milliseconds: '100ms'

• In a string, as seconds: '0.1s'

The second argument, delay , has the same syntax as duration . For example:

• Wait for 100 ms and then run for 200 ms: '0.2s 100ms'

The third argument, easing , controls how the animation accelerates and decelerates during its runtime. For example, ease-in causes the animation to begin slowly, and to pick up speed as it progresses.

• Wait for 100 ms, run for 200 ms. Use a deceleration curve to start out fast and slowly decelerate to a resting point:

        
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        0.2s 100ms ease-out
      

• Run for 200 ms, with no delay. Use a standard curve to start slow, speed up in the middle, and then decelerate slowly at the end:

        
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        0.2s ease-in-out
      

• Start immediately, run for 200 ms. Use an acceleration curve to start slow and end at full velocity:

        
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  The code sample is missing.
      

  0.2s ease-in

This example provides a state transition from open to closed with a 1-second transition between states.

      
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      transition('open => closed', [
  animate('1s')
]),
    

In the preceding code snippet, the => operator indicates unidirectional transitions, and <=> is bidirectional. Within the transition, animate() specifies how long the transition takes. In this case, the state change from open to closed takes 1 second, expressed here as 1s .

This example adds a state transition from the closed state to the open state with a 0.5-second transition animation arc.

      
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      transition('closed => open', [
  animate('0.5s')
]),
    

Define animations and attach to an HTML template link

Animations are defined in the metadata of the component that controls the HTML element to be animated.

Define the animation link

Put the code that defines your animations under the animations: property within the @Component() decorator.

      
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      @Component({
  selector: 'app-open-close',
  animations: [
    trigger('openClose', [
      // ...
      state('open', style({
        height: '200px',
        opacity: 1,
        backgroundColor: 'yellow'
      })),
      state('closed', style({
        height: '100px',
        opacity: 0.8,
        backgroundColor: 'blue'
      })),
      transition('open => closed', [
        animate('1s')
      ]),
      transition('closed => open', [
        animate('0.5s')
      ]),
    ]),
  ],
  templateUrl: 'open-close.component.html',
  styleUrls: ['open-close.component.css']
})
export class OpenCloseComponent {
  isOpen = true;

  toggle() {
    this.isOpen = !this.isOpen;
  }

}
    

When an animation trigger for a component is defined, attach it to an element in the template. Wrap the trigger name in brackets and precede it with an @ symbol. Bind the trigger to a template expression using standard Angular property binding syntax. The triggerName is the name of the trigger, and expression evaluates to a defined animation state.

      
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      <div [@triggerName]="expression">…</div>;
    

The animation is executed or triggered when the expression value changes to a new state.

The following code snippet binds the trigger to the value of the isOpen property.

      
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      <nav>
  <button type="button" (click)="toggle()">Toggle Open/Close</button>
</nav>

<div [@openClose]="isOpen ? 'open' : 'closed'" class="open-close-container">
  <p>The box is now {{ isOpen ? 'Open' : 'Closed' }}!</p>
</div>
    

In this example, when the isOpen expression evaluates to a defined state of open or closed , it notifies the trigger openClose of a state change. Then it's up to the openClose code to handle the state change and kick off a state change animation.

For elements entering or leaving a page (inserted or removed from the DOM), you can make the animations conditional. For example, use *ngIf with the animation trigger in the HTML template.

Introduction to Angular animations link

Animation provides the illusion of motion: HTML elements change styling over time. Well-designed animations can make your application more fun and straightforward to use, but they aren't just cosmetic. Animations can improve your application and user experience in a number of ways:

• Without animations, web page transitions can seem abrupt and jarring
• Motion greatly enhances the user experience, so animations give users a chance to detect the application's response to their actions
• Good animations intuitively call the user's attention to where it is needed

Typically, animations involve multiple style transformations over time. An HTML element can move, change color, grow or shrink, fade, or slide off the page. These changes can occur simultaneously or sequentially. You can control the timing of each transformation.

Angular's animation system is built on CSS functionality, which means you can animate any property that the browser considers animatable. This includes positions, sizes, transforms, colors, borders, and more. The W3C maintains a list of animatable properties on its CSS Transitions page.

About this guide link

This guide covers the basic Angular animation features to get you started on adding Angular animations to your project.

The features described in this guide —and the more advanced features described in the related Angular animations guides— are demonstrated in an example application available as a live example / download example .

Prerequisites link

The guide assumes that you're familiar with building basic Angular apps, as described in the following sections:

• Tutorial
• Architecture Overview

Getting started link

The main Angular modules for animations are @angular/animations and @angular/platform-browser . When you create a new project using the CLI, these dependencies are automatically added to your project.

To get started with adding Angular animations to your project, import the animation-specific modules along with standard Angular functionality.

Step 1: Enabling the animations module link

Import BrowserAnimationsModule , which introduces the animation capabilities into your Angular root application module.

      
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      import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';

@NgModule({
  imports: [
    BrowserModule,
    BrowserAnimationsModule
  ],
  declarations: [ ],
  bootstrap: [ ]
})
export class AppModule { }
    

Step 2: Importing animation functions into component files link

If you plan to use specific animation functions in component files, import those functions from @angular/animations .

      
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      import { Component, HostBinding } from '@angular/core';
import {
  trigger,
  state,
  style,
  animate,
  transition,
  // ...
} from '@angular/animations';
    

Step 3: Adding the animation metadata property link

In the component file, add a metadata property called animations: within the @Component() decorator. You put the trigger that defines an animation within the animations metadata property.

      
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      @Component({
  selector: 'app-root',
  templateUrl: 'app.component.html',
  styleUrls: ['app.component.css'],
  animations: [
    // animation triggers go here
  ]
})
    

Animating a transition link

Let's animate a transition that changes a single HTML element from one state to another. For example, you can specify that a button displays either Open or Closed based on the user's last action. When the button is in the open state, it's visible and yellow. When it's the closed state, it's translucent and blue.

In HTML, these attributes are set using ordinary CSS styles such as color and opacity. In Angular, use the style() function to specify a set of CSS styles for use with animations. Collect a set of styles in an animation state, and give the state a name, such as open or closed .

      
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      ng g component open-close
    

Animation state and styles link

Use Angular's state() function to define different states to call at the end of each transition. This function takes two arguments: A unique name like open or closed and a style() function.

Use the style() function to define a set of styles to associate with a given state name. You must use camelCase for style attributes that contain dashes, such as backgroundColor or wrap them in quotes, such as 'background-color' .

Let's see how Angular's state() function works with the style⁣­(⁠) function to set CSS style attributes. In this code snippet, multiple style attributes are set at the same time for the state. In the open state, the button has a height of 200 pixels, an opacity of 1, and a yellow background color.

      
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      // ...
state('open', style({
  height: '200px',
  opacity: 1,
  backgroundColor: 'yellow'
})),
    

In the following closed state, the button has a height of 100 pixels, an opacity of 0.8, and a background color of blue.

      
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      state('closed', style({
  height: '100px',
  opacity: 0.8,
  backgroundColor: 'blue'
})),
    

Transitions and timing link

In Angular, you can set multiple styles without any animation. However, without further refinement, the button instantly transforms with no fade, no shrinkage, or other visible indicator that a change is occurring.

To make the change less abrupt, you need to define an animation transition to specify the changes that occur between one state and another over a period of time. The transition() function accepts two arguments: The first argument accepts an expression that defines the direction between two transition states, and the second argument accepts one or a series of animate() steps.

Use the animate() function to define the length, delay, and easing of a transition, and to designate the style function for defining styles while transitions are taking place. Use the animate() function to define the keyframes() function for multi-step animations. These definitions are placed in the second argument of the animate() function.

Animation metadata: duration, delay, and easing link

The animate() function (second argument of the transition function) accepts the timings and styles input parameters.

The timings parameter takes either a number or a string defined in three parts.

      
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      animate (duration)
    

or

      
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      animate ('duration delay easing')
    

The first part, duration , is required. The duration can be expressed in milliseconds as a number without quotes, or in seconds with quotes and a time specifier. For example, a duration of a tenth of a second can be expressed as follows:

• As a plain number, in milliseconds: 100

• In a string, as milliseconds: '100ms'

• In a string, as seconds: '0.1s'

The second argument, delay , has the same syntax as duration . For example:

• Wait for 100ms and then run for 200ms: '0.2s 100ms'

The third argument, easing , controls how the animation accelerates and decelerates during its runtime. For example, ease-in causes the animation to begin slowly, and to pick up speed as it progresses.

• Wait for 100ms, run for 200ms. Use a deceleration curve to start out fast and slowly decelerate to a resting point: '0.2s 100ms ease-out'

• Run for 200ms, with no delay. Use a standard curve to start slow, accelerate in the middle, and then decelerate slowly at the end: '0.2s ease-in-out'

• Start immediately, run for 200ms. Use an acceleration curve to start slow and end at full velocity: '0.2s ease-in'

This example provides a state transition from open to closed with a 1-second transition between states.

      
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      transition('open => closed', [
  animate('1s')
]),
    

In the preceding code snippet, the => operator indicates unidirectional transitions, and <=> is bidirectional. Within the transition, animate() specifies how long the transition takes. In this case, the state change from open to closed takes 1 second, expressed here as 1s .

This example adds a state transition from the closed state to the open state with a 0.5-second transition animation arc.

      
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      transition('closed => open', [
  animate('0.5s')
]),
    

Triggering the animation link

An animation requires a trigger , so that it knows when to start. The trigger() function collects the states and transitions, and gives the animation a name, so that you can attach it to the triggering element in the HTML template.

The trigger() function describes the property name to watch for changes. When a change occurs, the trigger initiates the actions included in its definition. These actions can be transitions or other functions, as we'll see later on.

In this example, we'll name the trigger openClose , and attach it to the button element. The trigger describes the open and closed states, and the timings for the two transitions.

Defining animations and attaching them to the HTML template link

Animations are defined in the metadata of the component that controls the HTML element to be animated. Put the code that defines your animations under the animations: property within the @Component() decorator.

      
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      @Component({
  selector: 'app-open-close',
  animations: [
    trigger('openClose', [
      // ...
      state('open', style({
        height: '200px',
        opacity: 1,
        backgroundColor: 'yellow'
      })),
      state('closed', style({
        height: '100px',
        opacity: 0.8,
        backgroundColor: 'blue'
      })),
      transition('open => closed', [
        animate('1s')
      ]),
      transition('closed => open', [
        animate('0.5s')
      ]),
    ]),
  ],
  templateUrl: 'open-close.component.html',
  styleUrls: ['open-close.component.css']
})
export class OpenCloseComponent {
  isOpen = true;

  toggle() {
    this.isOpen = !this.isOpen;
  }

}
    

When you've defined an animation trigger for a component, attach it to an element in that component's template by wrapping the trigger name in brackets and preceding it with an @ symbol. Then, you can bind the trigger to a template expression using standard Angular property binding syntax as shown below, where triggerName is the name of the trigger, and expression evaluates to a defined animation state.

      
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      <div [@triggerName]="expression">…</div>;
    

The animation is executed or triggered when the expression value changes to a new state.

The following code snippet binds the trigger to the value of the isOpen property.

      
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      <nav>
  <button type="button" (click)="toggle()">Toggle Open/Close</button>
</nav>

<div [@openClose]="isOpen ? 'open' : 'closed'" class="open-close-container">
  <p>The box is now {{ isOpen ? 'Open' : 'Closed' }}!</p>
</div>
    

In this example, when the isOpen expression evaluates to a defined state of open or closed , it notifies the trigger openClose of a state change. Then it's up to the openClose code to handle the state change and kick off a state change animation.

For elements entering or leaving a page (inserted or removed from the DOM), you can make the animations conditional. For example, use *ngIf with the animation trigger in the HTML template.

Code review link

Here are the code files discussed in the transition example.

      
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      @Component({
  selector: 'app-open-close',
  animations: [
    trigger('openClose', [
      // ...
      state('open', style({
        height: '200px',
        opacity: 1,
        backgroundColor: 'yellow'
      })),
      state('closed', style({
        height: '100px',
        opacity: 0.8,
        backgroundColor: 'blue'
      })),
      transition('open => closed', [
        animate('1s')
      ]),
      transition('closed => open', [
        animate('0.5s')
      ]),
    ]),
  ],
  templateUrl: 'open-close.component.html',
  styleUrls: ['open-close.component.css']
})
export class OpenCloseComponent {
  isOpen = true;

  toggle() {
    this.isOpen = !this.isOpen;
  }

}
    

Summary link

You learned to add animation to a transition between two states, using style() and state() along with animate() for the timing.

Learn about more advanced features in Angular animations under the Animation section, beginning with advanced techniques in transition and triggers.

Animations API summary link

The functional API provided by the @angular/animations module provides a domain-specific language (DSL) for creating and controlling animations in Angular applications. See the API reference for a complete listing and syntax details of the core functions and related data structures.

More on Angular animations link

You might also be interested in the following:

• Transition and triggers
• Complex animation sequences
• Reusable animations
• Route transition animations