What is the best way to monitor and react to individual changes in a form array within an Angular application?

  constructor(private stockService: StockService, private fb: FormBuilder, public dialog: MatDialog, public snackBar: MatSnackBar, private supplierService: SupplierService, private productService: ProductService) { 
    this.stockForm = this.fb.group ({ //form validator for create and update
      _id: [ "" ],
      stockItem: this.fb.array([ this.createItem() ])
    });
  }

  createItem(): FormGroup { //form array for order Items
    return this.fb.group({
      supplierId: [ "", Validators.compose([Validators.required, Validators.pattern(/^[a-f\d]{24}$/i), Validators.minLength(24), Validators.maxLength(24)]) ],
      productId: [ "", Validators.compose([Validators.required, Validators.pattern(/^[a-f\d]{24}$/i), Validators.minLength(24), Validators.maxLength(24)]) ],
      productQuantity: [ "", Validators.compose([Validators.required, Validators.pattern(/^[0-9]\d*$/), Validators.min(1), Validators.max(99999)]) ]
    });
  }

i'm seeking to monitor changes in individual elements within a form array. I currently have code that observes all elements in the form array for changes.

  onChanges(): void {
    this.stockForm.get('stockItem').valueChanges.subscribe(val => {
    });
  }

Answer №1

To monitor value changes, you can use the following methods:

  1. Form Changes binding | Triggers on any field value change

_

onChanges(): void {
  this.myForm.valueChanges.subscribe(val => {
    //Perform actions here
  });
}
  1. Specific field binding | Triggers on specific field change

_

onChanges(): void {
  this.myForm.get('FIELD_NAME').valueChanges.subscribe(val => {

  });
}

Hopefully, this explanation helps. Remember to use the field name instead of the form name.

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