> For the complete documentation index, see [llms.txt](https://redd.gitbook.io/react-advanced-form/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://redd.gitbook.io/react-advanced-form/components/form/callbacks/on-first-change.md).

# onFirstChange

## Specification

A callback function dispatched once when the first value change of a field happens.

## Parameters

| Param        | Type     | Description                                   |
| ------------ | -------- | --------------------------------------------- |
| `event`      | `Event`  | Change event reference.                       |
| `prevValue`  | `any`    | Previous value of the changed field.          |
| `nextValue`  | `any`    | Next value of the changed field.              |
| `fieldProps` | `Object` | Props of the field that triggered the change. |
| `fields`     | `Object` | Reference to all fields in the form.          |
| `form`       | `Object` | Form component reference.                     |

## Example

```jsx
import React from 'react'
import { Form } from 'react-advanced-form'

export default class Example extends React.Component {
  handleFirstChange = ({ event, prevValue, nextValue, fieldProps, fields, form }) => {
    console.log('Field `%s` made the form dirty.', fieldProps.name)
  }

  render() {
    return (
      <Form onFirstChange={this.handleFirstChange}>
        {/* Fields here */}
      </Form>
    )
  }
}
```