在 Angular 库中创建时，instanceof 返回 false

Question

When created an object in an Angular Library, instanceof returns false.

import {
  Component,
  OnInit
} from '@angular/core';
import {
  FormControl,
} from '@angular/forms';
import {genControl} from 'test-lib';                        // import a function from my own library.

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss']
})
export class AppComponent implements OnInit{

  constructor() {
  }

  ngOnInit() {

    const fcA = genControl();                               // Create a FormControl in Angular Library
    const fcB = new FormControl('');

    if (fcA instanceof FormControl) {
      console.log('fcA is instanceof FormControl');
    } else {
      console.log('fcA is not instanceof FormControl');     // displays this.
    }

    if (fcB instanceof FormControl) {
      console.log('fcB is instanceof FormControl');         // displays this.
    } else {
      console.log('fcB is not instanceof FormControl');
    }

  }
}

test-lib is an Angular Library project build as this post . The code for genControl is as below.

import {FormControl} from '@angular/forms';

export function genControl(): FormControl {
  return new FormControl('');
}

The output of the code above is as follows.

fcA is not instanceof FormControl
fcB is instanceof FormControl

Why fcA is not an instance of FormControl ? How should I fix for fcA will be instance of FormControl ?

Angular version is same between main project AppComponent and Angular Library genControl , which is 9.1.11.

Answer 1

As @andriishupta mentioned, this is because the app and the lib imports FormControl from different files. I should specify paths in tsconfig.json as follows.

  "compilerOptions": {
        :
    "paths": {
      "@angular/*": [
        "./node_modules/@angular/*"
      ]
    }
  },