Basic Concepts and Terminology
This page introduces the basic concepts and terminology used in the @tanstack/react-form library. Familiarizing yourself with these concepts will help you better understand and work with the library.
Form Factory
The Form Factory is responsible for creating form instances with a shared configuration. It is created using the createFormFactory function, which accepts a configuration object with default values for the form fields. This shared configuration allows you to create multiple form instances with consistent behavior.
Example:
const formFactory = createFormFactory<Person>({
defaultValues: {
firstName: '',
lastName: '',
hobbies: [],
},
})
const formFactory = createFormFactory<Person>({
defaultValues: {
firstName: '',
lastName: '',
hobbies: [],
},
})
Form Instance
A Form Instance is an object that represents an individual form and provides methods and properties for working with the form. You create a form instance using the useForm hook provided by the form factory. The hook accepts an object with an onSubmit function, which is called when the form is submitted.
const form = formFactory.useForm({
onSubmit: async ({ value }) => {
// Do something with form data
console.log(value)
},
})
const form = formFactory.useForm({
onSubmit: async ({ value }) => {
// Do something with form data
console.log(value)
},
})
You may also create a form instance without going through the formFactory by using the standalone useForm API:
const form = useForm<Person>({
onSubmit: async ({ value }) => {
// Do something with form data
console.log(value)
},
defaultValues: {
firstName: '',
lastName: '',
hobbies: [],
},
})
const form = useForm<Person>({
onSubmit: async ({ value }) => {
// Do something with form data
console.log(value)
},
defaultValues: {
firstName: '',
lastName: '',
hobbies: [],
},
})
Field
A Field represents a single form input element, such as a text input or a checkbox. Fields are created using the form.Field component provided by the form instance. The component accepts a name prop, which should match a key in the form's default values. It also accepts a children prop, which is a render prop function that takes a field object as its argument.
Example:
<form.Field
name="firstName"
children={(field) => (
<>
<input
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
<FieldInfo field={field} />
</>
)}
/>
<form.Field
name="firstName"
children={(field) => (
<>
<input
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
<FieldInfo field={field} />
</>
)}
/>
Field State
Each field has its own state, which includes its current value, validation status, error messages, and other metadata. You can access a field's state using the field.state property.
Example:
const { value, error, touched, isValidating } = field.state
const { value, error, touched, isValidating } = field.state
There are three field states can be very useful to see how the user interacts with a field. A field is "touched" when the user clicks/tabs into it, "pristine" until the user changes value in it, and "dirty" after the value has been changed. You can check these states via the isTouched, isPristine and isDirty flags, as seen below.
const { isTouched, isPristine, isDirty } = field.state.meta
const { isTouched, isPristine, isDirty } = field.state.meta
Important note for users coming from React Hook Form: the isDirty flag in TanStack/form is different from the flag with the same name in RHF. In RHF, isDirty = true, when the form's values are different from the original values. If the user changes the values in a form, and then changes them again to end up with values that match the form's default values, isDirty will be false in RHF, but true in TanStack/form. The default values are exposed both on the form's and the field's level in TanStack/form (form.options.defaultValues, field.options.defaultValue), so you can write your own isDefaultValue() helper if you need to emulate RHF's behavior.`
Field API
The Field API is an object passed to the render prop function when creating a field. It provides methods for working with the field's state.
Example:
<input
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
<input
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
Validation
@tanstack/react-form provides both synchronous and asynchronous validation out of the box. Validation functions can be passed to the form.Field component using the validators prop.
Example:
<form.Field
name="firstName"
validators={{
onChange: ({ value }) =>
!value
? 'A first name is required'
: value.length < 3
? 'First name must be at least 3 characters'
: undefined,
onChangeAsync: async ({ value }) => {
await new Promise((resolve) => setTimeout(resolve, 1000))
return value.includes('error') && 'No "error" allowed in first name'
},
}}
children={(field) => (
<>
<input
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
<FieldInfo field={field} />
</>
)}
/>
<form.Field
name="firstName"
validators={{
onChange: ({ value }) =>
!value
? 'A first name is required'
: value.length < 3
? 'First name must be at least 3 characters'
: undefined,
onChangeAsync: async ({ value }) => {
await new Promise((resolve) => setTimeout(resolve, 1000))
return value.includes('error') && 'No "error" allowed in first name'
},
}}
children={(field) => (
<>
<input
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
<FieldInfo field={field} />
</>
)}
/>
Validation Adapters
In addition to hand-rolled validation options, we also provide adapters like @tanstack/zod-form-adapter, @tanstack/yup-form-adapter, and @tanstack/valibot-form-adapter to enable usage with common schema validation tools like Zod, Yup, and Valibot.
Example:
import { zodValidator } from '@tanstack/zod-form-adapter'
import { z } from 'zod'
// ...
<form.Field
name="firstName"
validatorAdapter={zodValidator}
validators={{
onChange: z.string().min(3, 'First name must be at least 3 characters'),
onChangeAsyncDebounceMs: 500,
onChangeAsync: z.string().refine(
async (value) => {
await new Promise((resolve) => setTimeout(resolve, 1000))
return !value.includes('error')
},
{
message: "No 'error' allowed in first name",
},
),
}}
/>
import { zodValidator } from '@tanstack/zod-form-adapter'
import { z } from 'zod'
// ...
<form.Field
name="firstName"
validatorAdapter={zodValidator}
validators={{
onChange: z.string().min(3, 'First name must be at least 3 characters'),
onChangeAsyncDebounceMs: 500,
onChangeAsync: z.string().refine(
async (value) => {
await new Promise((resolve) => setTimeout(resolve, 1000))
return !value.includes('error')
},
{
message: "No 'error' allowed in first name",
},
),
}}
/>
Reactivity
@tanstack/react-form offers various ways to subscribe to form and field state changes, such as the form.useStore hook, the form.Subscribe component, and the form.useField hook. These methods allow you to optimize your form's rendering performance by only updating components when necessary.
Example:
<form.Subscribe
selector={(state) => [state.canSubmit, state.isSubmitting]}
children={([canSubmit, isSubmitting]) => (
<button type="submit" disabled={!canSubmit}>
{isSubmitting ? '...' : 'Submit'}
</button>
)}
/>
<form.Subscribe
selector={(state) => [state.canSubmit, state.isSubmitting]}
children={([canSubmit, isSubmitting]) => (
<button type="submit" disabled={!canSubmit}>
{isSubmitting ? '...' : 'Submit'}
</button>
)}
/>
Array Fields
Array fields allow you to manage a list of values within a form, such as a list of hobbies. You can create an array field using the form.Field component with the mode="array" prop.
When working with array fields, you can use the fields pushValue, removeValue, swapValues and moveValue methods to add, remove, and swap values in the array.
Example:
<form.Field
name="hobbies"
mode="array"
children={(hobbiesField) => (
<div>
Hobbies
<div>
{!hobbiesField.state.value.length
? 'No hobbies found.'
: hobbiesField.state.value.map((_, i) => (
<div key={i}>
<form.Field
name={`hobbies[${i}].name`}
children={(field) => {
return (
<div>
<label htmlFor={field.name}>Name:</label>
<input
id={field.name}
name={field.name}
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
<button
type="button"
onClick={() => hobbiesField.removeValue(i)}
>
X
</button>
<FieldInfo field={field} />
</div>
)
}}
/>
<form.Field
name={`hobbies[${i}].description`}
children={(field) => {
return (
<div>
<label htmlFor={field.name}>Description:</label>
<input
id={field.name}
name={field.name}
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
<FieldInfo field={field} />
</div>
)
}}
/>
</div>
))}
</div>
<button
type="button"
onClick={() =>
hobbiesField.pushValue({
name: '',
description: '',
yearsOfExperience: 0,
})
}
>
Add hobby
</button>
</div>
)}
/>
<form.Field
name="hobbies"
mode="array"
children={(hobbiesField) => (
<div>
Hobbies
<div>
{!hobbiesField.state.value.length
? 'No hobbies found.'
: hobbiesField.state.value.map((_, i) => (
<div key={i}>
<form.Field
name={`hobbies[${i}].name`}
children={(field) => {
return (
<div>
<label htmlFor={field.name}>Name:</label>
<input
id={field.name}
name={field.name}
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
<button
type="button"
onClick={() => hobbiesField.removeValue(i)}
>
X
</button>
<FieldInfo field={field} />
</div>
)
}}
/>
<form.Field
name={`hobbies[${i}].description`}
children={(field) => {
return (
<div>
<label htmlFor={field.name}>Description:</label>
<input
id={field.name}
name={field.name}
value={field.state.value}
onBlur={field.handleBlur}
onChange={(e) => field.handleChange(e.target.value)}
/>
<FieldInfo field={field} />
</div>
)
}}
/>
</div>
))}
</div>
<button
type="button"
onClick={() =>
hobbiesField.pushValue({
name: '',
description: '',
yearsOfExperience: 0,
})
}
>
Add hobby
</button>
</div>
)}
/>
These are the basic concepts and terminology used in the @tanstack/react-form library. Understanding these concepts will help you work more effectively with the library and create complex forms with ease.
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