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@jaredpalmer jaredpalmer released this 25 Oct 16:18
v2.0.1
80a0a34

Formik 2 Migration Guide

Breaking Changes

Minimum Requirements

  • Since Formik 2 is built on top of React Hooks, you must be on React 16.8.x or higher
  • Since Formik 2 uses the unknown type, you must be on TypeScript 3.0 or higher

resetForm

There is only one tiny breaking change in Formik 2.x. Luckily, it probably won't impact verry many people. Long story short, because we introduced initialErrors, initialTouched, initialStatus props, resetForm's signature has changed. It now accepts the next initial state of Formik (instead of just the next initial values).

v1

resetForm(nextValues);

v2

resetForm({ values: nextValues /* errors, touched, etc ... */ });

What's New?

Checkboxes and Select multiple

Similarly to Angular, Vue, or Svelte, Formik 2 "fixes" React checkboxes and multi-selects with built-in array binding and boolean behavior. This was one of the most confusing things for people in Formik 1.x.

import React from 'react';
import { Formik, Field, Form } from 'formik';
import { Debug } from './Debug';

const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));

const CheckboxExample = () => (
  <div>
    <h1>Checkboxes</h1>
    <p>
      This example demonstrates how to properly create checkboxes with Formik.
    </p>
    <Formik
      initialValues={{
        isAwesome: false,
        terms: false,
        newsletter: false,
        jobType: ['designer'],
        location: [],
      }}
      onSubmit={async values => {
        await sleep(1000);
        alert(JSON.stringify(values, null, 2));
      }}
    >
      {({ isSubmitting, getFieldProps, handleChange, handleBlur, values }) => (
        <Form>
          {/* 
            This first checkbox will result in a boolean value being stored.
          */}
          <div className="label">Basic Info</div>
          <label>
            <Field type="checkbox" name="isAwesome" />
            Are you awesome?
          </label>
          {/* 
            Multiple checkboxes with the same name attribute, but different
            value attributes will be considered a "checkbox group". Formik will automagically
            bind the checked values to a single array for your benefit. All the add and remove
            logic will be taken care of for you.
          */}
          <div className="label">
            What best describes you? (check all that apply)
          </div>
          <label>
            <Field type="checkbox" name="jobType" value="designer" />
            Designer
          </label>
          <label>
            <Field type="checkbox" name="jobType" value="developer" />
            Developer
          </label>
          <label>
            <Field type="checkbox" name="jobType" value="product" />
            Product Manager
          </label>
          {/*
           You do not _need_ to use <Field>/useField to get this behaviorr, 
           using handleChange, handleBlur, and values works as well. 
          */}
          <label>
            <input
              type="checkbox"
              name="jobType"
              value="founder"
              checked={values.jobType.includes('founder')}
              onChange={handleChange}
              onBlur={handleBlur}
            />
            CEO / Founder
          </label>

          {/* 
           The <select> element will also behave the same way if 
           you pass `multiple` prop to it. 
          */}
          <label htmlFor="location">Where do you work?</label>
          <Field
            component="select"
            id="location"
            name="location"
            multiple={true}
          >
            <option value="NY">New York</option>
            <option value="SF">San Francisco</option>
            <option value="CH">Chicago</option>
            <option value="OTHER">Other</option>
          </Field>
          <label>
            <Field type="checkbox" name="terms" />I accept the terms and
            conditions.
          </label>
          {/* Here's how you can use a checkbox to show / hide another field */}
          {!!values.terms ? (
            <div>
              <label>
                <Field type="checkbox" name="newsletter" />
                Send me the newsletter <em style={{ color: 'rebeccapurple' }}>
                  (This is only shown if terms = true)
                </em>
              </label>
            </div>
          ) : null}
          <button type="submit" disabled={isSubmitting}>
            Submit
          </button>
          <Debug />
        </Form>
      )}
    </Formik>
  </div>
);

export default CheckboxExample;

useField()

Just what you think, it's like <Field>, but with a hook. See docs for usage.

useFormikContext()

A hook that is equivalent to connect().

<Field as>

<Field/> now accepts a prop called as which will inject onChange, onBlur, value etc. directly through to the component or string. This is useful for folks using Emotion or Styled components as they no longer need to clean up component's render props in a wrapped function.

Misc

  • FormikContext is now exported
  • validateOnMount?: boolean = false
  • initialErrors, initialTouched, initialStatus have been added
// <input className="form-input" placeHolder="Jane"  />
<Field name="firstName" className="form-input" placeholder="Jane" />

// <textarea className="form-textarea"/></textarea>
<Field name="message" as="textarea"  className="form-input"/>

// <select className="my-select"/>
<Field name="colors" as="select" className="my-select">
  <option value="red">Red</option>
  <option value="green">Green</option>
  <option value="blue">Blue</option>
</Field>

// with styled-components/emotion
const MyStyledInput = styled.input`
  padding: .5em;
  border: 1px solid #eee;
  /* ... */
`
const MyStyledTextarea = MyStyledInput.withComponent('textarea');

// <input className="czx_123" placeHolder="google.com"  />
<Field name="website" as={MyStyledInput} placeHolder="google.com"/>

// <textarea  placeHolder="Post a message..." rows={5}></textarea>
<Field name="message" as={MyStyledTextArea} placeHolder="Post a message.." rows={4}/>

getFieldProps(nameOrProps)

There are two useful additions to FormikProps, getFieldProps and getFieldMeta. These are Kent C. Dodds-esque prop getters that can be useful if you love prop drilling, are not using the context-based API's, or if you are building a custom useField.

export interface FieldInputProps<Value> {
  /** Value of the field */
  value: Value;
  /** Name of the field */
  name: string;
  /** Multiple select? */
  multiple?: boolean;
  /** Is the field checked? */
  checked?: boolean;
  /** Change event handler */
  onChange: FormikHandlers['handleChange'];
  /** Blur event handler */
  onBlur: FormikHandlers['handleBlur'];
}

getFieldMeta(name)

Given a name it will return an object:

export interface FieldMetaProps<Value> {
  /** Value of the field */
  value: Value;
  /** Error message of the field */
  error?: string;
  /** Has the field been visited? */
  touched: boolean;
  /** Initial value of the field */
  initialValue?: Value;
  /** Initial touched state of the field */
  initialTouched: boolean;
  /** Initial error message of the field */
  initialError?: string;
}

Deprecation Warnings

All render props have been deprecated with a console warning.

For <Field>, <FastField>, <Formik>,<FieldArray>, the render prop has been deprecated with a warning as it will be removed in future versions. Instead, use a child callback function. This deprecation is meant to parallel React Context Consumer's usage.

- <Field name="firstName" render={props => ....} />
+ <Field name="firstName">{props => ... }</Field>
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