Route transition animations in Angular - Step-by-Step Execution

Concept Flow - Route transition animations

User triggers route change

↓

Angular Router starts transition

↓

Animation trigger activates

↓

Old component animates out

↓

New component animates in

↓

Transition completes, new route displayed

Shows how Angular triggers animations during route changes, animating old and new components smoothly.

Execution Sample

Angular

import { trigger, transition, style, animate, query } from '@angular/animations';

export const fadeAnimation = trigger('routeAnimations', [
  transition('* <=> *', [
    style({ position: 'relative' }),
    query(':enter, :leave', [
      style({
        position: 'absolute',
        top: 0,
        left: 0,
        width: '100%',
        height: '100%'
      })
    ], { optional: true }),
    query(':enter', [
      style({ opacity: 0 })
    ], { optional: true }),
    query(':leave', [
      animate('300ms ease-in-out', style({ opacity: 0 }))
    ], { optional: true }),
    query(':enter', [
      animate('300ms ease-in-out', style({ opacity: 1 }))
    ], { optional: true })
  ])
]);

Defines a simple fade animation triggered on any route change.

Execution Table

Step	Trigger	Animation State	Action	Result
1	User clicks link to new route	No animation	Router starts route change	Old component visible
2	Route change detected	Animation trigger fires	Old component animates out (fade out)	Old component fades out
3	Old component animation ends	Prepare new component	New component loads hidden	New component ready but invisible
4	New component animation starts	Animate in	New component animates in (fade in)	New component becomes visible
5	Animation completes	Animation ends	Transition finishes	New route fully displayed
6	Idle	No animation	Waiting for next route change	Stable UI

💡 Animation completes and new route is fully displayed, waiting for next user action.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
oldComponentVisibility	visible	fading out	hidden	hidden	hidden
newComponentVisibility	hidden	hidden	hidden	fading in	visible
animationState	none	running fade out	preparing fade in	running fade in	none

Key Moments - 3 Insights

Why does the old component animate out before the new one animates in?

Because Angular runs the 'leave' animation first to smoothly remove the old view before showing the new one, as shown in execution_table steps 2 and 3.

What triggers the animation to start on route change?

The Angular Router detects the route change and triggers the animation defined by the 'routeAnimations' trigger, as seen in step 2 of the execution_table.

Why is the new component initially hidden before animating in?

It is hidden to avoid flicker and to allow the fade-in animation to run smoothly, as shown in step 3 where the new component is ready but invisible.

Visual Quiz - 3 Questions

Look at the execution_table, what is the animationState at step 4?

A running fade out

B preparing fade in

C running fade in

D none

💡 Hint

Check the 'Animation State' column at step 4 in the execution_table.

At which step does the old component become hidden?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at 'oldComponentVisibility' in variable_tracker after each step.

If the animation duration changes from 300ms to 600ms, what changes in the execution_table?

A Steps remain same but animation actions take longer

B Animation trigger fires later

C New component loads earlier

D Old component does not animate out

💡 Hint

Duration affects timing but not the order of steps in execution_table.

Concept Snapshot

Angular route transition animations:
- Use trigger() with transition() to define animations
- Animate old component out before new component in
- Use '* <=> *' to animate all route changes
- Animations run on route change events
- Helps smooth UI changes between pages

Full Transcript

When a user changes routes in Angular, the router detects this and triggers animations defined by the developer. First, the old component animates out, usually fading or sliding away. Then the new component loads hidden and animates in, creating a smooth transition effect. This process involves animation triggers that listen for route changes and run animations in sequence. Variables track visibility and animation states to manage the UI during the transition. This approach improves user experience by avoiding abrupt content changes.