RangeError: Invalid array length while i test my angular code

Question

Code is working properly there is no issue on that, but While I test my angular code I got this following error.

what i have to add to get rid of this error. anyone please help me on this. i know array size get exceeded but how to fix that? RangeError: Invalid array length

component.ts

 this.columns = Array.from(Array(this.nbColumn - 1 > 0 ? this.nbColumn - 1 : 0 ).keys())

spec.ts

describe('HomeComponent', () => {
      let component: HomeComponent;
      let fixture: ComponentFixture<HomeComponent>;
    
      beforeEach(waitForAsync(() => {
        TestBed.configureTestingModule({
          imports:[HttpClientModule,RouterTestingModule,MatSnackBarModule],
          declarations: [ HomeComponent ],
          providers:[ ]
        })
        .compileComponents();
      }));
    
      beforeEach(() => {
        fixture = TestBed.createComponent(HomeComponent);
        component = fixture.componentInstance;
        fixture.detectChanges();
      });
    
      it('should create', () => {
        expect(component).toBeTruthy();
      });
    });

Edited: I have added my spec file

can you show your unit test (spec) file ? As suggested, you may have mismocked some values. — Random
– Random, Commented Mar 15, 2023 at 9:49
Indeed, your unit test is empty. detectChanges will run your ngOnInit. You have to mock all your services so their method return a specific value, which would allow the ngOnInit() method to run without errors. — Random
– Random, Commented Mar 15, 2023 at 10:01
@Random , thanks for your feedback .As i am new to angular , can you please help me with add some example — web_in
– web_in, Commented Mar 15, 2023 at 10:05
Sorry, but if you are new to Angular, this code is too complex to help you easily. You should follow a unit test course. — Random
– Random, Commented Mar 15, 2023 at 10:10

Joosep Parts · Accepted Answer · 2023-03-15 08:17:09Z

The JavaScript exception "Invalid array length" occurs when specifying an array length that is either negative, a floating number or exceeds the maximum supported by the platform (i.e. when creating an Array or ArrayBuffer, or when setting the length property).

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/Invalid_array_length

I don't know exactly where is home.component.ts line 52 char 23 on your image, because you haven't provided code lines, but the trace probably points to this part (just an educated guess):

Observe when variable nbColumn in the snippet changes:

    this.columns = Array(this.nbColumn - 1)
      .fill(0)
      .map((x, i) => i);

nbColumn = 1

columns = [];
nbColumn = 1;

this.columns = Array(this.nbColumn - 1).fill(0).map((x, i) => i);

console.log(this.columns)

nbColumn = 0

columns = [];
nbColumn = 0;

this.columns = Array(this.nbColumn - 1).fill(0).map((x, i) => i);

console.log(this.columns)

Probably your test doesn't populate some properties as it does in the actual application. Find out why it is so or fix the likely problematic area Array(this.nbColumn - 1).

Maybe assert that an array is always produced?

this.columns = Array.from(Array(this.nbColumn - 1 > 0 ? this.nbColumn - 1 : 0 ).keys())

More on how to use Array.from() here: https://stackoverflow.com/a/33352604/15439733

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