Type inference determines useful static types from declarations and usage, reducing annotations while exposing mismatches early. Angular’s inject function infers the type associated with an InjectionToken, avoiding the wordier and less secure @Inject pattern. A misspelled property can otherwise leave the token correctly injected while the property type is wrong. section 3.2.3
Reactive forms provide another practical use. Since Angular 14, form controls infer the structure of their values instead of defaulting to any. The inferred value remains Partial because fields may be absent, even when validators are present; after checking validity, code may narrow or cast the value. Templates still catch mismatched control names, such as using email when the control is misspelled emali. section 4.3.2
Application-wide constants and typed employee forms
Define a root-provided Constants InjectionToken for shared values such as dateFormat, then inject it with inject(Constants) so the property type follows the token. In an HRMS employee form, use dot notation such as form.controls.email; Angular’s inferred control type reports a misspelled control name before the template runs. section 3.2.3 section 4.3.2
Listing 3.7 Injection token for application-wide constants
import { InjectionToken } from '@angular/core';
const CONSTANTS = { #1
dateFormat: 'dd/MM/yyyy',
};
export const Constants = new InjectionToken('Constants', {
factory() {
return CONSTANTS; #2
},
providedIn: 'root', #3
});
Shows a root-provided InjectionToken whose factory returns application-wide constants, providing the typed dependency consumed through inject. section 3.2.3
