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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteAngular lifecycle hooks control when a component runs setup, responds to input changes, and cleans up; template event bindings handle browser interactions; and component outputs send custom events from a child to its parent. These are separate mechanisms with different timing and data paths. Choose based on what is changing: a component, a DOM event, or a route navigation.
How Angular component lifecycle works
A component’s lifecycle runs from creation through change detection and rendering to destruction. Angular checks components in a tree traversal, visiting each component once during that pass. Its lifecycle guide cautions against changing state in the middle of that traversal, because doing so can lead to inconsistent checks or errors.
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The constructor is ordinary class construction, not a lifecycle hook. After construction, Angular initializes inputs, runs change-detection and content/view hooks as applicable, renders the DOM, and eventually destroys the component. Hook timing matters: use the hook that matches what needs to be ready, rather than treating them as interchangeable callbacks.
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| Need | Use | Timing and caution |
|---|---|---|
| Initialize once using initial input values | ngOnInit |
Runs once after Angular initializes the component’s inputs and before it initializes the component’s own template. |
| Respond when an input changes | ngOnChanges |
Runs when inputs change, including their initial values. Use it for work that must track input updates rather than only initial setup. |
| Perform custom checking during change detection | ngDoCheck |
Runs frequently. Use only when you have a specific need, since repeated work can affect performance. |
In practice, use ngOnInit for one-time setup that depends on inputs, and ngOnChanges when new input values should trigger updated behavior. Neither is a substitute for the other: the first is a one-time initialization point; the second responds to input changes.
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When content, view, or rendered DOM is ready
Content and view hooks apply when Angular has initialized the corresponding projected content or component view, and can be useful when query results become available. The checked versions run repeatedly as Angular checks content or view bindings.
ngAfterContentInitandngAfterViewInitrun after their respective content or view is initialized. Changing component state in these hooks can causeExpressionChangedAfterItHasBeenCheckedError.ngAfterContentCheckedandngAfterViewCheckedrun repeatedly. Avoid expensive or unnecessary work in them.
For code that must run after Angular has rendered components to the DOM, the rendering callbacks afterNextRender and afterEveryRender are distinct from instance hooks. They are application-wide callbacks, must be registered in an injection context, and do not run during server-side rendering or build-time prerendering.
Clean up work when a component is destroyed
Use ngOnDestroy for cleanup immediately before Angular destroys a component, such as releasing resources or stopping ongoing work. Angular also provides DestroyRef: call its onDestroy() method to register a cleanup callback, keeping setup and cleanup close together or passing destruction behavior to another function. Its destroyed property can help prevent work from running against an instance that has already been destroyed.
Handle browser events in a template
Bind a native event by placing its name in parentheses in the template. Pass $event when the handler needs the browser event object. Angular’s event-listener guide also supports key filters and global targets.
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<button (click)="save()">Save</button>
<input (keyup.enter)="submit()">
<input (keyup)="onKey($event)">Use a key filter such as (keyup.enter) to respond to a common key without checking it in the handler. Modifier combinations such as (keyup.shift.enter) are also supported; available modifiers include alt, control, meta, and shift. The code suffix matches the physical key code rather than the character produced, which can matter across keyboard layouts or input languages.
For a global listener, prefix the event target with window:, document:, or body:. If the handler should suppress the browser’s default response, call event.preventDefault() explicitly.
Send a custom event from a child to its parent
Use a component output when a child needs to notify its parent about a component-specific action. Angular recommends the output() API for new projects; the decorator-based @Output() and EventEmitter API remains supported. The outputs guide shows the current pattern:
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// Child component
panelClosed = output<void>();
closePanel() {
this.panelClosed.emit();
}
// Parent template
<expandable-panel (panelClosed)="savePanelState()" />An output can carry a value as well. The parent receives the emitted value as $event:
// Child component
selectionChanged = output<string>();
choose(value: string) {
this.selectionChanged.emit(value);
}
// Parent template
<child-picker (selectionChanged)="onSelection($event)" />Output names are case-sensitive; Angular recommends camelCase and advises against names that collide with native DOM events. Custom outputs do not bubble through the DOM. If an event needs to pass through an intermediate component, that component must explicitly emit or forward it. When subscribing to an output programmatically, the subscription has an unsubscribe() method; Angular automatically cleans up output subscriptions when it destroys a component that has subscribers.
How Router events differ
Router events describe navigation, not component lifecycle or browser input. Subscribe to Router.events when code needs to react to navigation phases or outcomes, such as NavigationStart, route recognition, guard or resolver activity, NavigationEnd, NavigationCancel, or NavigationError. Check the event type and respond only to the phase relevant to the task. See Angular’s routing lifecycle and events guide.
Quick decision guide and common mistakes
| What you need to react to | Angular mechanism | Typical pattern |
|---|---|---|
| Initial component setup based on inputs | Lifecycle hook | ngOnInit |
| A changed input | Lifecycle hook | ngOnChanges |
| A click, key press, or other browser interaction | Template listener | (click), (keyup.enter) |
| A child component’s custom notification | Component output | output() and a parent listener |
| A navigation phase or result | Router event stream | Router.events |
- Do not put expensive work in hooks that run on every check, such as
ngDoCheckand the checked content/view hooks. - Do not assume that changing state in a content or view initialization hook is harmless; it can trigger an expression-changed error.
- Do not rely on relative hook ordering between a component and directives on the same element; Angular does not guarantee it.
- Do not expect a child output to bubble like a DOM event. Forward it explicitly if an intermediate component must pass it along.
Angular’s current unversioned guides describe these APIs. If maintaining an application on a specific Angular release, verify behavior and API availability against documentation for that version before relying on newer APIs.
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