# onChange()

### Overview

This is a [\<Feathery.Form>](/develop/react/api-guide/form.md) prop and callback function to run custom logic when a field value is changed. It's called every time the user changes one or multiple field values. This function can be asynchronous.

### Usage <a href="#usage" id="usage"></a>

You can use `onChange` to log or update form state when the user modifies it. It takes a single [Context](#context-api) object that provides form-related state and handlers.

```
import { init, Form } from '@feathery/react';

function App() {
  // Initialize Feathery
  init('SDKKey', 'bob@feathery.io');

  // Show the `aBcDeF` Feathery form
  return <Form
    formId='aBcDeF'
    // Custom form step onChange logic
    onChange={(context) => {
      if (context.trigger.id === 'is-it-birthday' && context.fields['is-it-birthday']) {
          showBirthdaySurprise();
      }
    }}
  />
}
```

### Context API

|                   Key                   |                Type                | Description                                                                                                                                                                                                                               |
| :-------------------------------------: | :--------------------------------: | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| [Form Context](/develop/context-api.md) |                                    | Consistently available form state and functions                                                                                                                                                                                           |
|            `integrationData`            |          `optional object`         | Third-party metadata may be passed back through this property. If `trigger` equals `addressSelect`, this object returns the  Google Places address ID (`id`), the components of its address, and the latitude / longitude of the address. |
|                `trigger`                | [triggerData](#triggerdata-object) | Info of the element that triggered the field value change.                                                                                                                                                                                |
|            `valueRepeatIndex`           |              `integer`             | Specifies which item (0-indexed) in the field value changed if there are multiple items. If an item was removed, the index will be -1.                                                                                                    |

#### `integrationData` Definition <a href="#triggerdata-object" id="triggerdata-object"></a>

&#x20;If `trigger` equals `addressSelect`, this change event was triggered by the user selecting an [Address Line 1](/platform/build-forms/elements/fields/address/street-address-line-1.md) dropdown option. In that case, `integrationData` contains the address's Google Places address ID (`id`), its individual components, and the latitude / longitude.

#### `triggerData` Definition <a href="#triggerdata-object" id="triggerdata-object"></a>

|      Key      |              Type             | Description                                                                                                                                                                        |
| :-----------: | :---------------------------: | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
|      `id`     |            `string`           | The ID of the field that changed.                                                                                                                                                  |
|     `type`    | `enum {field, addressSelect}` | What triggered the field value change. Either a form field was modified or an [Address Line 1](/platform/build-forms/elements/fields/address.md) autocomplete option was selected. |
| `repeatIndex` |           `integer`           | If the element whose value changed repeats, this specifies which repetition it is. This value is 0-indexed and equals 0 if the element doesn't repeat.                             |


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