typescript 46 lines · 8 steps

Layered config with an Angular InjectionToken

An injection token supplies analytics defaults that a provider factory layers runtime and override values on top of.

Explained by highlit

Angular Intermediate dependency-injection configuration factory-provider immutability validation

1import { InjectionToken, inject, Provider, isDevMode } from '@angular/core';
2import { WINDOW } from './window.token';
3 
4export interface AnalyticsConfig {
5  readonly endpoint: string;
6  readonly flushIntervalMs: number;
7  readonly sampleRate: number;
8  readonly debug: boolean;
9}
10 
11export const ANALYTICS_DEFAULTS: AnalyticsConfig = {
12  endpoint: 'https://collect.example.com/v1/events',
13  flushIntervalMs: 5_000,
14  sampleRate: 1,
15  debug: false,
16};
17 
18export const ANALYTICS_CONFIG = new InjectionToken<AnalyticsConfig>(
19  'ANALYTICS_CONFIG',
20  {
21    providedIn: 'root',
22    factory: () => ({ ...ANALYTICS_DEFAULTS, debug: isDevMode() }),
23  },
24);
25 
26export function provideAnalytics(overrides: Partial<AnalyticsConfig> = {}): Provider {
27  return {
28    provide: ANALYTICS_CONFIG,
29    useFactory: (): AnalyticsConfig => {
30      const win = inject(WINDOW);
31      const runtime = (win as unknown as { __ANALYTICS__?: Partial<AnalyticsConfig> }).__ANALYTICS__ ?? {};
32      const merged: AnalyticsConfig = {
33        ...ANALYTICS_DEFAULTS,
34        debug: isDevMode(),
35        ...runtime,
36        ...overrides,
37      };
38 
39      if (merged.sampleRate < 0 || merged.sampleRate > 1) {
40        throw new Error(`ANALYTICS_CONFIG: sampleRate must be within [0, 1], got ${merged.sampleRate}`);
41      }
42 
43      return Object.freeze(merged);
44    },
45  };
46}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1A tree-shakable InjectionToken with a factory gives you a sensible default without requiring any explicit provider registration.
2Spread order encodes precedence — later sources win, so runtime and caller overrides beat static defaults.
3Validating and freezing config at construction turns bad input into an early, loud failure instead of a silent bug.

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