Limiting input values in Angular 8 number fields

I am working on an Angular 8 application and I want to restrict the user from entering any value outside the range of 0-100 in a number input field.

My initial idea was to implement something like this:

<input type="number" [ngModel]="value" (ngModelChange)="validateValue($event)">

and

value = 100;

validateValue(event: number) {
    if (event > 100) {
      this.value = 100;
    } else if (event < 0) {
      this.value = 0;
    } else {
      this.value = event;
    }
}

It works perfectly when manually entering a value such as deleting the last digit and typing a new one. However, it does not work correctly when using the step arrows or selecting the last digit and changing it directly.

I am puzzled as to why this behavior is occurring. Can anyone shed some light on this issue?

Answer №1

Recently encountered this issue myself. It seems that Angular doesn't take into account the max/min attributes specified on a number input field. These constraints only apply to the spinner buttons, which are controlled by the browser itself rather than Angular. In standard HTML/JavaScript, entering a value outside of the prescribed range renders it as 'undefined'; however, in Angular, such values are accepted.

To address this, here's a workaround that should meet your requirements; if you prefer an out-of-range value to be set to 'undefined' instead, simply eliminate the setTimeout() calls.

public realValue : number;
public min : number = 0;
public max : number = 100;

get value() : number {
    return this.realValue;
}

set value(newValue : number) {
    this.realValue = newValue;
    if(this.realValue < this.min){
        this.realValue = undefined;
        setTimeout(() => {this.realValue = this.min;});
    }
    else if(this.realValue > this.max){
        this.realValue = undefined;
        setTimeout(() => {this.realValue = this.max;});
    }
}
<input type="number" [(ngModel)]="value" [min]="min" [max]="max" (ngModelChange)="changeCallback()" />

By creating a virtual property with getter and setter methods, Angular is able to navigate its ngModel binding through your custom logic, ensuring that the value always remains within the defined boundaries, no matter how it is assigned. It appears necessary to briefly set the value to 'undefined'; for some reason, Angular didn't update the displayed value in the input field when directly assigning realValue to min or max. Through setting it to undefined and then utilizing setTimeout to assign the desired value seems to trigger an update, despite resulting in a peculiar blinking effect.

Answer №2

If you're looking for a solution, consider this approach:

let result;

  checkNumber(event: number) {

    if (event > 100) {
      result = 100;
    } else if (event < 0) {
      result = 0;
    } else {
      result = event;
    }
  }

In your HTML template :

<input type="number" [(ngModel)]="result" (ngModelChange)="checkNumber($event)">

This method has been effective in my experience :)

Answer №3

Experiment using the Min and Max attributes.

<input type="number" min="1" max="5">

By incorporating these attributes, users will be constrained from selecting a number outside of the specified range.

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