React Form

React Form allow for handling user input and managing form submission. React provides controlled and uncontrolled components for handling forms.

1. Controlled Components

In controlled components, form data is handled by the component’s state.

Functional Components with Hooks

import React, { useState } from 'react';

export default function MyForm() {
  const [name, setName] = useState('');
  const [age, setAge] = useState('');

  const handleNameChange = (event) => {
    setName(event.target.value);
  };

  const handleAgeChange = (event) => {
    setAge(event.target.value);
  };

  const handleSubmit = (event) => {
    event.preventDefault();
    alert(`Name: ${name}, Age: ${age}`);
  };

  return (
    <form onSubmit={handleSubmit}>
      <label>
        Name:
        <input type="text" value={name} onChange={handleNameChange} />
      </label>
      <br />
      <label>
        Age:
        <input type="number" value={age} onChange={handleAgeChange} />
      </label>
      <br />
      <button type="submit">Submit</button>
    </form>
  );
}

2. Uncontrolled Components

In uncontrolled components, form data is handled by the DOM itself.

Using ref in Functional Components

import React, { useRef } from 'react';

export default function MyForm() {
  const nameRef = useRef(null);
  const ageRef = useRef(null);

  const handleSubmit = (event) => {
    event.preventDefault();
    alert(`Name: ${nameRef.current.value}, Age: ${ageRef.current.value}`);
  };

  return (
    <form onSubmit={handleSubmit}>
      <label>
        Name:
        <input type="text" ref={nameRef} />
      </label>
      <br />
      <label>
        Age:
        <input type="number" ref={ageRef} />
      </label>
      <br />
      <button type="submit">Submit</button>
    </form>
  );
}

Handling Form Validation

Form validation can be added by checking the form data before submission.

Functional Components with Hooks

import React, { useState } from 'react';

export default function MyForm() {
  const [formState, setFormState] = useState({ name: '', age: '' });
  const [errors, setErrors] = useState({ name: '', age: '' });

  const handleChange = (event) => {
    const { name, value } = event.target;
    setFormState((prevState) => ({
      ...prevState,
      [name]: value,
    }));
  };

  const validateForm = () => {
    let valid = true;
    let errors = {};

    if (!formState.name) {
      valid = false;
      errors.name = 'Name is required';
    }

    if (!formState.age) {
      valid = false;
      errors.age = 'Age is required';
    } else if (isNaN(formState.age)) {
      valid = false;
      errors.age = 'Age must be a number';
    }

    setErrors(errors);
    return valid;
  };

  const handleSubmit = (event) => {
    event.preventDefault();
    if (validateForm()) {
      alert(`Name: ${formState.name}, Age: ${formState.age}`);
    }
  };

  return (
    <form onSubmit={handleSubmit}>
      <label>
        Name:
        <input type="text" name="name" value={formState.name} onChange={handleChange} />
        {errors.name && <span>{errors.name}</span>}
      </label>
      <br />
      <label>
        Age:
        <input type="number" name="age" value={formState.age} onChange={handleChange} />
        {errors.age && <span>{errors.age}</span>}
      </label>
      <br />
      <button type="submit">Submit</button>
    </form>
  );
}

create form through use react-hook-form library

install react-hook-form

npm install react-hook-form

create form through react-hook-form with validation

import React from 'react';
import { useForm } from 'react-hook-form';

export default function SignUp(){

    const {register,handleSubmit,formState: { errors }} = useForm();

    const signupSubmit = async (data) =>{
      console.log(data);
    }

    return(
        <div>
        <h1>Signup Form</h1>
        <form onSubmit={handleSubmit(signupSubmit)}>

        <div className='container'>

            <div className="row">
             FirstName:
             <input type="text" id="firstName" {...register('firstName',{required:{value:true,message:"First Name is required"},maxLength:{value:10, message:"First Name should be less than or equal to 10"}})} />
             {errors.firstName && <p className='alert alert-danger'>{errors.firstName?.message}</p> }
            </div>
            <div className="row my-2">
             LastName:
             <input type="text" id="lastName" {...register('lastName',{required:{value:true,message:"Last Name is required"},maxLength:{value:10, message:"Last Name should be less than or equal to 10"}})} />
             {errors.lastName && <p className='alert alert-danger'>{errors.lastName?.message}</p> }
            </div>
            <div><button className='btn btn-primary'>Submit</button></div>

        </div>
        </form>
        </div>
    )
}

React Form – Interview Questions

Reactjs React Form – Objective Questions (MCQs)

Related React Form Topics