Form Input Number Validator In Reactive Form

Form Input Number Validator In Reactive Form

Introduction to Reactive Forms and Form Input Number Validation

In web development, forms are an integral part of user interaction and getting input from users. Reactive forms are a way of creating forms in Angular that are predictable and very flexible. Reactive forms use reactive programming to watch for changes and events from the user and react to them accordingly.

One of the challenges with form inputs is validating the user’s input to ensure it meets certain criteria. In particular, validating number inputs can be problematic as numbers come in various formats and can include decimal points, negative signs, and more. Fortunately, Angular’s reactive forms provide built-in validators for number inputs, making it easy to enforce input constraints and ensure data quality.

Form Input Number Validator in Reactive Form

Understanding the Angular Validators API for Form Validation

When it comes to validating forms in Angular, the Validators API is a powerful tool that developers can leverage to ensure that user input meets certain requirements. The Validators API provides a set of pre-built validators that can be easily used in reactive forms, making it simpler for developers to add validation rules to form fields.

To use the Validators API, first you need to import it from ‘@angular/forms’:

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

From there, you can use the various validators available in the Validators API, such as:

  • Validators.required for making a field required
  • Validators.minLength for setting a minimum length for a field
  • Validators.maxLength for setting a maximum length for a field
  • Validators.pattern for enforcing a regex pattern on a field
  • for validating an email address

To add a validator to a form control in a reactive form, you can simply pass it as an argument to the FormControl constructor, like this:

import { Component } from ‘@angular/core’;
import { FormControl, Validators } from ‘@angular/forms’;

selector: ‘app-example’,
template: `

Please enter a valid value.

export class ExampleComponent {
myControl = new FormControl(”, [

In this example, the myControl form control is being initialized with four different validators: Validators.required, Validators.minLength, Validators.maxLength, and Validators.pattern. This means that the user input will be validated against all of these rules, and an error message will be displayed if any of them are not met.

Using the Validators API can greatly simplify form validation in Angular, and can help ensure that user input is accurate and consistent across your application.

How to Implement Number Validation for Reactive Forms in Angular

If you are working with reactive forms in Angular and need to implement number validation, there are a few steps you can take to ensure that the user input is valid. Here are the steps:

  1. Import the Validators module from ‘@angular/forms’
  2. Create a new form control using the FormControl class and pass in an initial value and a validator. In this case, we will use the Validators.number validator to ensure that the value is a number.
  3. Use the form control in your form and display an error message if the user input is not a number.

Here is an example of how to implement number validation for a reactive form in Angular:

import { Component } from '@angular/core';
import { FormControl, FormGroup, Validators } from '@angular/forms';

  selector: 'app-number-validation',
  templateUrl: './number-validation.component.html'
export class NumberValidationComponent {
  numberForm = new FormGroup({
    numberInput: new FormControl('', Validators.number)

In this example, we are creating a new form control using the FormControl class and passing in the Validators.number validator as the second parameter. This will ensure that the user input is a number.

Next, we are using the numberForm in our number-validation.component.html file:

<form [formGroup]="numberForm">
  <label for="numberInput">Number Input:</label>
  <input type="text" formControlName="numberInput">
  <div *ngIf="numberForm.get('numberInput').hasError('number')">
    Please enter a valid number.

In this HTML code, we are using the formControlName directive to access the numberInput form control that we created earlier. We are also using the *ngIf directive to display an error message if the user input is not a number.

That’s it! With these steps, you can easily implement number validation for reactive forms in Angular.

Building Custom Validators for Number Input Validation in Angular Forms

When it comes to creating forms in Angular, input validation is essential to ensure data accuracy and integrity. Angular Forms provide a wide range of validators that developers can utilize to validate user input. However, there may be cases where these built-in validators might not suffice. In such cases, custom validators can be created to complement the existing validators.

In this blog post, we will focus on creating custom validators for number input validation in Angular Forms. Numeric input validation is a common requirement in many applications, and we will explore how to create a custom validator that can handle such scenarios.

The first step is to create a custom validator function that will implement our validation logic. This function will receive the control as an input and return a validation result object.

Once the validator function is defined, we can use it with our reactive form controls. We can either add it to the form control constructor directly or to the existing validators’ array of the form control.

Leveraging custom validators can help us tailor the validation logic specific to our project’s needs. It provides greater flexibility and control over the validation process, resulting in a more efficient and robust application.

Handling Invalid Input and Displaying Error Messages in Reactive Forms

When working with reactive forms in Angular, it is important to handle invalid user input and display appropriate error messages. This can help users to understand what they did wrong and how to correct their mistakes.

To display error messages, first, we need to define validators for our form fields. Validators are functions that validate user input and return an error object if the input is invalid. We can then bind these validators to our form controls using the Validators class.

Once a form control has a validator, we can check the control’s valid property to see if the input is valid. If it is not valid, we can access the errors property to get information about the validation error. We can then display an error message to the user based on the error information.

One way to display error messages is to use Angular’s built-in ngIf directive. We can use ngIf to conditionally display error messages based on whether a form control is valid or not. For example:


My Control is required.
My Control must be at least {{ myForm.controls[‘myControl’].errors.min.min }}.
My Control must be at most {{ myForm.controls[‘myControl’].errors.max.max }}.


In this example, we use ngIf to check if the myControl form control is invalid and has been touched or is dirty (meaning the user has tried to submit the form or has interacted with the control). We then display error messages based on the type of error.

By displaying error messages for invalid form input, we can provide a better user experience and help users to submit correct and valid information.

Best Practices for Implementing Form Input Number Validation in Angular

If you’re building an Angular application with forms that include numerical input fields, it’s essential to implement form input number validation to ensure data accuracy and prevent user errors. Here are some best practices to follow when implementing number validation in Angular:

  • Use the appropriate input type: When creating the numerical input fields in your form, use the “number” input type to ensure that users can only input numeric values.
  • Set appropriate validators: Use Angular’s built-in validators to set minimum, maximum, and required values for numerical input fields. This will prevent users from entering values that fall outside the specified range or leaving required fields empty.
  • Display clear error messages: When a user enters an invalid value, display a clear error message that describes the error and how to fix it. This will help users correct errors efficiently.
  • Validate input on submit: When users submit the form, validate all input fields and display error messages if necessary. This will ensure that all data submitted is accurate and meets the specified requirements.
  • Consider using third-party libraries: If you need to implement more complex numerical validations, consider using third-party libraries such as ng2-validation or ngx-mask.

Conclusion: Why Form Input Validation is Crucial for User Experience and Data Integrity

Form input validation is crucial for the overall experience of the user as well as the data integrity of the application. Validating the user’s input ensures that the data being submitted is accurate and meets the requirements of the database. This helps in reducing errors and improving the consistency and quality of the data.

Additionally, form input validation plays a crucial role in improving the user experience. By providing immediate feedback to the user, it helps in guiding them towards correct input and preventing mistakes. This helps in reducing frustration and increasing the trust and engagement of the user with the application.

In conclusion, form input validation is a critical component for any application that deals with user input. It not only helps in maintaining the integrity of the data but also ensures a positive user experience. Therefore, it is important for developers to implement effective form input validation techniques to enhance the usability and robustness of the application.

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