React Formik

What?

Formik is a small library that helps you deal with forms in React. Formik keeps track of form's state and handles form submission.

Why?

Managing form data or form state
Form submission
Form validation and displaying error messages

How to use formik?

Import the `useFormik` hook

import { useFormik } from "formik";

Create a formik instance

const formik = useFormik({
        initialValues: {
            name: "",
            email: "",
            password: "",
        },
    });

The initialValues 'name', 'email', 'password' correspond to the name attribute of the input fields.

Add the onChange and value props to the input fields

<form>
    <input
        type="password"
        name="password"
        value={formik.values.password}
        onChange={formik.handleChange}
    />
    <button type="submit">Submit</button>
</form>

formik.values.password is the value of the input field. And password is the name attribute of the input field.
handleChange is a function (formik helper) that updates the form state.
formik.values is an object that contains the form state and will give us access to the form data.

Add the onSubmit event to the form

<form onSubmit={formik.handleSubmit}>
</form>

formik.handleSubmit is a function that handles form submission.

Add the onSubmit function to the formik instance

const formik = useFormik({
        initialValues: {
            name: "",
            email: "",
            password: "",
        },
        onSubmit: (values) => {
            console.log(values);
        },
    });

values is an object that contains the form data that we were referring to using formik.values.

Validate the form

Formik lets you define a validation function that will run when the form is submitted. This validation function needs to be assigned to the validate property of the formik instance in the useFormik hook.

const formik = useFormik({
    initialValues: {
      name: "",
      email: "",
      password: "",
    },
    onSubmit: (values) => {
      console.log("Values: ", values);
    },
    validate: (values) => {
      // errors.name, errors.email, errors.password
      //name, email, password are the name attributes of the input fields
      const errors: any = {};
      if (!values.name) {
        errors.name = "Required";
      }
      if (!values.email) {
        errors.email = "Required";
      } 
      if (!values.password) {
        errors.password = "Required";
      }
      return errors;
    },
  });

Display the error messages

{
    formik.errors.name ? (
        <div className="text-red-500 text-sm mt-1">{formik.errors.name}</div>
    ) : null
}

To make sure the error is shown only for visited fields, add the onBlur prop to the input fields with the value formik.handleBlur.

<input
    type="text"
    name="name"
    id="name"
    onChange={formik.handleChange}
    value={formik.values.name}
    onBlur={formik.handleBlur}
    placeholder="Emelia Erickson"
    className=""
/>

We can keep track of the visited fields using the touched property of the formik instance.

{
    formik.touched.name && formik.errors.name ? (
        <div className="text-red-500 text-sm mt-1">{formik.errors.name}</div>
    ) : null
}

Yup

To make the form validation more robust, we can use the Yup library. Yup is a JavaScript schema builder for value parsing and validation.

Install Yup

npm install yup

Import Yup

import * as Yup from "yup";

Create a validation schema

const validationSchema = Yup.object({
    name: Yup.string().required("Name is required"),
    email: Yup.string().email("Invalid email address").required("Email is required"),
    password: Yup.string().required("Password is required"),
});

The object method of Yup is used to create a schema object. The schema object is used to define the validation rules for the form fields.

Pass the validation schema to the `useFormik` hook

const formik = useFormik({
    initialValues: {
        name: "",
        email: "",
        password: "",
    },
    onSubmit: (values) => {
        console.log("Values: ", values);
    },
    validationSchema: validationSchema,
});

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learning-react-formik's Introduction

React Formik

What?

Why?

How to use formik?

Import the useFormik hook

Create a formik instance

Add the onChange and value props to the input fields

Add the onSubmit event to the form

Add the onSubmit function to the formik instance

Validate the form

Display the error messages

Yup

Install Yup

Import Yup

Create a validation schema

Pass the validation schema to the useFormik hook

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Import the `useFormik` hook

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