What is the function of the Angular dependency injection mechanism?

I'm trying to grasp the inner workings of Angular/NestJs dependency injection. It's intriguing how the type of parameters gets lost when a Typescript class is constructed. For example:

type Dependency1 = {};
type Dependency2 = {};

class X {
    constructor(dependency: Dependency1){}
}

is transformed into

"use strict";
class X {
    constructor(dependency) { }
}

I'm curious about how the Angular Injector manages to replace the 'dependency' parameter with the correct instance of the Dependency class.

Answer №1

If the dependency injection resolution in Angular is reminiscent of Nest's (which was influenced by Angular), it likely relies on the function or class name for identification. In JavaScript, classes are essentially functions, and all functions have a .name property that can be used to retrieve the injection token. This token is then cross-referenced with the module container to ensure consistency with the corresponding token (class or custom provider).

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