Angular4 - prevent form submission when input is empty or value is less than 1

Question

Angular4 - prevent form submission when input is empty or value is less than 1

Currently, I am validating forms in an angular project and everything is working correctly. However, I want to take it a step further by disabling the form when the value in a specific textfield noWards is less than 1

Text Field

<input autocomplete="off" class="input100" type="text"   formControlName="noWards" [(ngModel)]="noWards">

Button

<button
    [disabled]="!questionsForm.valid || noWards.length < 3"
    [ngClass]="{'default':!questionsForm.valid}"
    (click)="goToNextStep()" class="contact100-form-btn">
      <span>
        Start
        <i class="fa fa-long-arrow-right m-l-7" aria-hidden="true"></i>
      </span>
    </button>

JavaScript

this.questionsForm = this.formBuilder.group({
            new: ['', Validators.required],
            noWards: ['', Validators.required],
            user: [''],
            pass: ['', Validators.required]
          });

javascript angular typescript

Answer 1

Answer №1

Rather than simply disabling the form inputs, it is not advisable as a potential security risk exists where a malicious user could manipulate this property in the DOM.

A more secure approach would involve removing the form inputs entirely and instead appending content tags (<span>, <p>, ...) directly to the DOM.

For example:

<input *ngIf="isEditable" type="text" ... [(ngModel)]="Name">
<span *ngIf="!isEditable"> {{Name}} </span>

Answer 2

Rather than simply disabling the form inputs, it is not advisable as a potential security risk exists where a malicious user could manipulate this property in the DOM.

A more secure approach would involve removing the form inputs entirely and instead appending content tags (<span>, <p>, ...) directly to the DOM.

For example:

<input *ngIf="isEditable" type="text" ... [(ngModel)]="Name">
<span *ngIf="!isEditable"> {{Name}} </span>

Answer 3

Answer №2

To achieve this functionality, utilize the (ngModelChange) event in your Angular application:

Below is the HTML code snippet:

<form [formGroup]="questionsForm">
    <input autocomplete="off" class="input100" type="text"   formControlName="noWards" [(ngModel)]="noWards" (ngModelChange)="isValid(noWards)" required>
<button
    [disabled]="!questionsForm.valid || isInputValid === false"
    (click)="goToNextStep()" class="contact100-form-btn">
    Test
    </button>
 </form>

In your TypeScript file, add the following property:

isInputValid: boolean = false;

Create a function called isValid() as shown below:

isValid(data) {
    var valid = /^([0-9]*[1-9][0-9]*)$/.test(data);
    if (valid) {
      this.isInputValid = true
    }
    else {
      this.isInputValid = false;
    }
  }

The condition for the [disabled] property should look like this:

[disabled]="!questionsForm.valid || isInputValid === false"

Here is a link to a working example on StackBlitz: Working Stackblitz Example

Answer 4

To achieve this functionality, utilize the (ngModelChange) event in your Angular application:

Below is the HTML code snippet:

<form [formGroup]="questionsForm">
    <input autocomplete="off" class="input100" type="text"   formControlName="noWards" [(ngModel)]="noWards" (ngModelChange)="isValid(noWards)" required>
<button
    [disabled]="!questionsForm.valid || isInputValid === false"
    (click)="goToNextStep()" class="contact100-form-btn">
    Test
    </button>
 </form>

In your TypeScript file, add the following property:

isInputValid: boolean = false;

Create a function called isValid() as shown below:

isValid(data) {
    var valid = /^([0-9]*[1-9][0-9]*)$/.test(data);
    if (valid) {
      this.isInputValid = true
    }
    else {
      this.isInputValid = false;
    }
  }

The condition for the [disabled] property should look like this:

[disabled]="!questionsForm.valid || isInputValid === false"

Here is a link to a working example on StackBlitz: Working Stackblitz Example

Answer 5

Answer №3

When working with reactive forms, it is recommended to utilize custom validators for field validation.

To ensure that only numbers are entered in a specific input field, you can use type="number".

In your TypeScript file, you should create a custom validator function like this:

  validatenoWards(control: FormControl) {
    if (control.value<1) {
      return { inValid: true };
    }
    return null;
  }

A custom validator should return null if the control value is valid; otherwise, it should return an object. Utilize it in the form group as shown below:

this.questionsForm = this.formBuilder.group({
            new: ['', Validators.required],
            noWards: ['', [this.validatenoWards,Validators.required]]],
            user: [''],
            pass: ['', Validators.required]
          });

To disable a button while the value of noWards is less than 1, simply use the disabled attribute based on the form's validity condition:

<button
    [disabled]="!questionsForm.valid"
    (click)="goToNextStep()" class="contact100-form-btn">
    Test
    </button>

You can implement any necessary logic within the custom validator to validate input fields and display customized messages according to the validation results. For further information on creating custom validators, refer to: Creating a Custom Validator.

Answer 6

When working with reactive forms, it is recommended to utilize custom validators for field validation.

To ensure that only numbers are entered in a specific input field, you can use type="number".

In your TypeScript file, you should create a custom validator function like this:

  validatenoWards(control: FormControl) {
    if (control.value<1) {
      return { inValid: true };
    }
    return null;
  }

A custom validator should return null if the control value is valid; otherwise, it should return an object. Utilize it in the form group as shown below:

this.questionsForm = this.formBuilder.group({
            new: ['', Validators.required],
            noWards: ['', [this.validatenoWards,Validators.required]]],
            user: [''],
            pass: ['', Validators.required]
          });

To disable a button while the value of noWards is less than 1, simply use the disabled attribute based on the form's validity condition:

<button
    [disabled]="!questionsForm.valid"
    (click)="goToNextStep()" class="contact100-form-btn">
    Test
    </button>

You can implement any necessary logic within the custom validator to validate input fields and display customized messages according to the validation results. For further information on creating custom validators, refer to: Creating a Custom Validator.

Answer 7

Answer №4

When dealing with the string length of the field called "noYards," you have the option to utilize the Validator Class from the Reactive Form Module. This can be achieved by using Validators.minLength() or Validators.maxLength() in the following manner:

this.questionsForm = this.formBuilder.group({
            new: ['', Validators.required],
            noWards: ['', Validators.minLength(1)],
            user: [''],
            pass: ['', Validators.required]
          });

Alternatively, if you need to validate the type number value for your field, you can create a Custom Validation function and apply it to your FormControl as demonstrated below:

import { AbstractControl } from '@angular/forms';

export function ValidateNoYards(control: AbstractControl) {
  if (control.value < 1) {
    return { validNoYards: false };
  }
  return true;
}

Make sure to include it in your Component like so:

this.questionsForm = this.formBuilder.group({
            new: ['', Validators.required],
            noWards: ['', ValidateNoYards],
            user: [''],
            pass: ['', Validators.required]
          });

This approach should meet your requirements.

Answer 8

When dealing with the string length of the field called "noYards," you have the option to utilize the Validator Class from the Reactive Form Module. This can be achieved by using Validators.minLength() or Validators.maxLength() in the following manner:

this.questionsForm = this.formBuilder.group({
            new: ['', Validators.required],
            noWards: ['', Validators.minLength(1)],
            user: [''],
            pass: ['', Validators.required]
          });

Alternatively, if you need to validate the type number value for your field, you can create a Custom Validation function and apply it to your FormControl as demonstrated below:

import { AbstractControl } from '@angular/forms';

export function ValidateNoYards(control: AbstractControl) {
  if (control.value < 1) {
    return { validNoYards: false };
  }
  return true;
}

Make sure to include it in your Component like so:

this.questionsForm = this.formBuilder.group({
            new: ['', Validators.required],
            noWards: ['', ValidateNoYards],
            user: [''],
            pass: ['', Validators.required]
          });

This approach should meet your requirements.

Angular4 - prevent form submission when input is empty or value is less than 1

Answer №1

Answer №2

Answer №3

Answer №4

`this.questionsForm = this.formBuilder.group({ new: ['', Validators.required], noWards: ['', Validators.minLength(1)], user: [''], pass: ['', Validators.required] });`

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