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What is the difference between useClass, useValue, useFactory, and useExisting?

Q: What is the difference between useClass, useValue, useFactory, and useExisting?

**Core concept.** They are the four **provider recipes** that tell Angular *how* to produce the value for a token. useClass instantiates a class, useValue supplies a ready-made value, useFactory computes one with a function (optionally using other deps), and useExisting **aliases** one token to another (sharing the same instance). useClass: new SomeClass() swap implementations useValue: literalValue con

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All four recipes

import { InjectionToken } from '@angular/core';

class Logger {}
class BetterLogger extends Logger {}
const API_URL = new InjectionToken<string>('apiUrl');

const providers = [
  { provide: Logger, useClass: BetterLogger },        // instantiate a class
  { provide: API_URL, useValue: 'https://api.example.com' }, // literal value
  { provide: 'CONFIG', useFactory: () => ({ debug: location.hostname === 'localhost' }) },
  { provide: 'AppLogger', useExisting: Logger },       // alias → same instance
];

export { providers };

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