Angular · Theory
ngOnInit runs once after inputs are set — load marks here, not in the constructor. ngOnDestroy — stop timers, unsubscribe. ngOnChanges — when @Input changes.
Board: constructor only assigns. ngOnInit calls marksService.list(). ngOnDestroy clears a setInterval. Trap: HTTP in constructor — inputs may still be undefined.
Init vs constructor. Destroy cleanup.
import { Component } from "@angular/core";
@Component({
selector: "app-root",
template: `
<h1>{{ title }}</h1>
<button (click)="toggle()">Toggle</button>
<p *ngIf="open">Panel open</p>
`,
})
export class AppComponent {
title = "Angular practice";
open = true;
toggle() {
this.open = !this.open;
}
}Lifecycle Hooks: toggle open. Say whether the panel is on screen after one click.