The combination of a reactive form and the latest object may result in a potential null or undefined

Is it possible to update a FormArray based on the values of two other controls?

After thorough checks, TypeScript is indicating issues with 'st' and 'sp'.

The object is potentially null.

Can someone identify the errors in this code?

let starterChanges$ = of(null);
    const starter = this.frm.get('starter');
    if (starter) {
      starterChanges$ = starter.valueChanges;
    }
    let spreadChanges$ = of(null);
    const spread = this.frm.get('spread');
    if (spread) {
      spreadChanges$ = spread.valueChanges;
    }
this.subscription.add(
      combineLatest([starterChanges$, spreadChanges$]).subscribe(([st, sp]) => {
        let current = 0;
        if (st !== null && sp !== null) {
          for (const control of this.orders.controls) {
            if (!current) {
              current = current + st + sp;
            } else {
              current = current + sp;
            }
            control.patchValue({ spread: current });
            control.disable();
          }
        }
      })
    );

Answer №1

This issue is most likely causing the trouble:

if (!current) {
  current = current + st + sp;
}

When !current is true, how can we perform the + operation? This would result in scenarios like null + st + sp, but what would be the outcome in such cases?

Answer №2

Give this test a shot:

if (st && sp) { ... }

Remember, you're verifying against null, but it could also be undefined.

Answer №3

(This response was submitted on behalf of the original poster to transfer it from the question section).

After some calculations, I found the solution using the following formula:

([st = 0, sp = 0])

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