Ng8103 Missingcontrolflowdirective Angular

Angular Control Flow Control flow directives (@if , @for , @switch ) render branches, lists, and cases in templates and replace the legacy *ngIf/*ngFor/[ngSwitch] for new code. Control Flow Essentials @if : Conditional blocks with optionalelse if /else .@for : Loops withtrack for stable identity and optional@empty for empty states.@switch : Selects and renders a matching case.- Preferred for new code in Angular 17+; legacy *ngIf /*ngFor /[ngSwitch] remain supported.

@if (score > 90) { <p>A</p> } @else if (score > 75) { <p>B</p> } @else { <p>C</p> } <ul> @for (it of items; track it.id) { <li>{{ it.label }}</li> } @empty { <li>No items</li> } </ul> @switch (status) { @case ('pending') { <p>Pending</p> } @case ('done') { <p>Done</p> } @default { <p>Unknown</p> } } Code explained @if ...

@else : Branches to render different blocks based on a condition.@for (...; track ...) : Iterates and usestrack to keep stable identities for DOM reuse.@switch/@case/@default : Selects and renders a matching case. Notes: - Related: See Templates, Directives, and Lists. - Use @for withtrack for stable list rendering. - Use @if ...; else for readable branches. Control Flow Basics Toggle content with @if ...; else . Iterate with @for and add a track expression for stable DOM updates.

@if (show) { <p>Visible</p> } @else { <p>Hidden</p> } @for (item of items; track item) { <li>{{ item }}</li> } Example Toggle content with @if , and render lists with @for using a track expression: Example import { bootstrapApplication } from '@angular/platform-browser'; import { Component, signal } from '@angular/core'; @Component({ selector: 'app-root', standalone: true, template: ` <h3>Control Flow</h3> <button (click)="show.set(!show())">Toggle</button> <button (click)="items.set([])">Clear</button> <button (click)="reset()">Reset</button> @if (show()) { <p>Visible</p> } @else { <p>Hidden</p> } <ul> @for (item of items(); track item) { <li>{{ item }}</li> } @empty { <li>No items</li> } </ul> ` }) export class App { show = signal(true); items = signal(['One','Two','Three']); reset() { this.items.set(['One','Two','Three']); } } bootstrapApplication(App); <app-root></app-root> Example explained @if ...

@else : Toggles the paragraph based on theshow() signal.@for ... track item : Renders the list from theitems() signal and preserves DOM withtrack .@empty : Displays a fallback when the list is empty.- Signals: Buttons update show anditems , which re-render the view. Notes: - Use track: Prefer tracking by a stable key (e.g., track it.id ) for lists of objects; for primitives,track item is fine. - Signals: Read signals with sig() in templates (e.g.,@if (flag()) ,@for (x of list()) ).

Legacy equivalence: In *ngFor , usetrackBy to matchtrack in@for . - Legacy syntax: *ngIf /*ngFor /[ngSwitch] remain supported; prefer@if /@for /@switch for new code. - Keep logic in TS: Compute flags and derived arrays in the component; keep templates simple. - No side effects: Avoid side effects inside control-flow blocks; update state in handlers/services.

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