use-field

use-field hook – manage single field state

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Usage

use-field hook is a simpler alternative to use-form, it can be used to manage state of a single input without the need to create a form:

Name

import { Button, TextInput } from '@mantine/core';
import { useField } from '@mantine/form';

function Demo() {
  const field = useField({
    initialValue: '',
    validate: (value) => (value.trim().length < 2 ? 'Value is too short' : null),
  });

  return (
    <>
      <TextInput {...field.getInputProps()} label="Name" placeholder="Enter your name" mb="md" />
      <Button onClick={field.validate}>Validate</Button>
    </>
  );
}

use-field API

use-field hook accepts the following options object as a single argument:

interface UseFieldInput<T> {
  /** Field mode, controlled by default */
  mode?: 'controlled' | 'uncontrolled';

  /** Initial field value */
  initialValue: T;

  /** Initial touched value */
  initialTouched?: boolean;

  /** Initial field error message */
  initialError?: React.ReactNode;

  /** Called with updated value when the field value changes */
  onValueChange?: (value: T) => void;

  /** Determines whether the field should be validated when value changes, false by default */
  validateOnChange?: boolean;

  /** Determines whether the field should be validated when it loses focus, false by default */
  validateOnBlur?: boolean;

  /** Determines whether the field should clear error message when value changes, true by default */
  clearErrorOnChange?: boolean;

  /** A function to validate field value, can be sync or async */
  validate?: (value: T) => React.ReactNode | Promise<React.ReactNode>;

  /** Field type, input by default */
  type?: 'input' | 'checkbox';

  /** A function to resolve validation error from the result returned from validate function, should return react node */
  resolveValidationError?: (error: unknown) => React.ReactNode;
}

And returns the following object:

export interface UseFieldReturnType<ValueType> {
  /** Returns props to pass to the input element */
  getInputProps: () => {
    /* props for input component */
  };

  /** Returns current input value */
  getValue: () => ValueType;

  /** Sets input value to the given value */
  setValue: (value: ValueType) => void;

  /** Resets field value to initial state, sets touched state to false, sets error to null */
  reset: () => void;

  /** Validates current input value when called */
  validate: () => Promise<React.ReactNode | void>;

  /** Set to true when async validate function is called, stays true until the returned promise resolves */
  isValidating: boolean;

  /** Current error message */
  error: React.ReactNode;

  /** Sets error message to the given react node */
  setError: (error: React.ReactNode) => void;

  /** Returns true if the input has been focused at least once */
  isTouched: () => boolean;

  /** Returns true if input value is different from the initial value */
  isDirty: () => boolean;

  /** Resets touched state to false */
  resetTouched: () => void;

  /** key that should be added to the input when mode is uncontrolled */
  key: number;
}

Validate on blur

To validate the field on blur, set validateOnBlur option to true:

Name

import { TextInput } from '@mantine/core';
import { useField } from '@mantine/form';

function Demo() {
  const field = useField({
    initialValue: '',
    validateOnBlur: true,
    validate: (value) => (value.trim().length < 2 ? 'Value is too short' : null),
  });

  return <TextInput {...field.getInputProps()} label="Name" placeholder="Enter your name" />;
}

Validate on change

To validate the field on change, set validateOnChange option to true:

import { TextInput } from '@mantine/core';
import { useField, isEmail } from '@mantine/form';

function Demo() {
  const field = useField({
    initialValue: '',
    validateOnChange: true,
    validate: isEmail('Invalid email'),
  });

  return <TextInput {...field.getInputProps()} label="Email" placeholder="Enter your email" />;
}

validate option accepts both async and sync functions, in both cases the function must return an error message that will be displayed to the user or null if the value is valid. To keep track of async validation state, use isValidating property:

Enter 'mantine'

import { Button, Loader, TextInput } from '@mantine/core';
import { useField } from '@mantine/form';

function validateAsync(value: string): Promise<string | null> {
  return new Promise((resolve) => {
    window.setTimeout(() => {
      resolve(value === 'mantine' ? null : 'Value must be "mantine"');
    }, 800);
  });
}

function Demo() {
  const field = useField({
    initialValue: '',
    validate: validateAsync,
  });

  return (
    <>
      <TextInput
        {...field.getInputProps()}
        label="Enter 'mantine'"
        placeholder="Enter 'mantine'"
        rightSection={field.isValidating ? <Loader size={18} /> : null}
        mb="md"
      />
      <Button onClick={field.validate}>Validate async</Button>
    </>
  );
}

Async validation can be used with validateOnBlur option, but not recommended with validateOnChange because it will trigger validation on every key press which may lead to race conditions:

Enter 'mantine'

import { Loader, TextInput } from '@mantine/core';
import { useField } from '@mantine/form';

function validateAsync(value: string): Promise<string | null> {
  return new Promise((resolve) => {
    window.setTimeout(() => {
      resolve(value === 'mantine' ? null : 'Value must be "mantine"');
    }, 800);
  });
}

function Demo() {
  const field = useField({
    initialValue: '',
    validateOnBlur: true,
    validate: validateAsync,
  });

  return (
    <TextInput
      {...field.getInputProps()}
      label="Enter 'mantine'"
      placeholder="Enter 'mantine'"
      rightSection={field.isValidating ? <Loader size={18} /> : null}
    />
  );
}

Touched and dirty

To get information about whether the field has been focused at least once, use isTouched method and to check if the value has been changed from the initial value, use isDirty method:

Name

Dirty: not dirty

Touched: not touched

import { Text, TextInput } from '@mantine/core';
import { useField } from '@mantine/form';

function Demo() {
  const field = useField({ initialValue: '' });

  return (
    <>
      <TextInput {...field.getInputProps()} label="Name" placeholder="Enter your name" mb="md" />

      <Text fz="sm">
        Dirty:{' '}
        <Text span inherit c={field.isDirty() ? 'red' : 'teal'}>
          {field.isDirty() ? 'dirty' : 'not dirty'}
        </Text>
      </Text>
      <Text fz="sm">
        Touched:{' '}
        <Text span inherit c={field.isTouched() ? 'red' : 'teal'}>
          {field.isTouched() ? 'touched' : 'not touched'}
        </Text>
      </Text>
    </>
  );
}

Clear error on change

By default, the error message is cleared when the value changes, to disable this behavior set clearErrorOnChange option to false:

Name

import { Button, TextInput } from '@mantine/core';
import { useField } from '@mantine/form';

function Demo() {
  const field = useField({
    initialValue: '',
    clearErrorOnChange: false,
    validate: (value) => (value.trim().length < 2 ? 'Value is too short' : null),
  });

  return (
    <>
      <TextInput {...field.getInputProps()} label="Name" placeholder="Enter your name" mb="md" />
      <Button onClick={field.validate}>Validate</Button>
    </>
  );
}

Uncontrolled mode

Uncontrolled mode of use-field hook works similar to uncontrolled mode of use-form. In uncontrolled mode, rerenders are minimized and the input value is managed by the input itself. It is useful if you experience performance issues with controlled mode, but in most cases controlled mode is recommended as it always provides up to date field information as React state.

Name

import { Button, TextInput } from '@mantine/core';
import { useField } from '@mantine/form';

function Demo() {
  const field = useField({
    mode: 'uncontrolled',
    initialValue: '',
    validate: (value) => (value.trim().length < 2 ? 'Value is too short' : null),
  });

  return (
    <>
      <TextInput
        {...field.getInputProps()}
        key={field.key}
        label="Name"
        placeholder="Enter your name"
        mb="md"
      />
      <Button onClick={field.validate}>Validate</Button>
    </>
  );
}

use-form

Uncontrolled mode

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