Check if a form field's value is lower than another in Angular reactive forms

Question

Check if a form field's value is lower than another in Angular reactive forms

In the form, I have a field called LDC along with two other fields named limit1 and limit2. My goal is to display an error message if either limit1 or limit2 exceeds the value of LDC, or if the sum of limit1 and limit2 surpasses LDC. I attempted to create a custom validator for this scenario, but it did not function as expected. I came across rxwebvalidators and I'm wondering if it's possible to customize error messages for these validators. Any assistance on this matter would be greatly appreciated. Thank you in advance.

typescript angular8

Answer 1

Answer №1

To easily handle errors, you can start by initializing a boolean variable like this:

hasError = false;

Then, you can listen to value changes for each field:

limit1.valueChanges().pipe(
   distinctUntilChanged()
).subscribe(value => {
  if (value + limit2.value < LDC) { // LDC is not defined here
    this.hasError = true;
  } else {
    this.hasError = false;
  }   
});

Repeat the same process for limit2 (assuming both are FormControls).

In your template, you can show or hide the error message using the ngIf directive like this:

<div>
  <input .... >
  <span *ngIf="hasError">Error message</span>
</div>

Answer 2

To easily handle errors, you can start by initializing a boolean variable like this:

hasError = false;

Then, you can listen to value changes for each field:

limit1.valueChanges().pipe(
   distinctUntilChanged()
).subscribe(value => {
  if (value + limit2.value < LDC) { // LDC is not defined here
    this.hasError = true;
  } else {
    this.hasError = false;
  }   
});

Repeat the same process for limit2 (assuming both are FormControls).

In your template, you can show or hide the error message using the ngIf directive like this:

<div>
  <input .... >
  <span *ngIf="hasError">Error message</span>
</div>

Check if a form field's value is lower than another in Angular reactive forms

Answer №1

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