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Last reviewed: April 2026.
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Detecting and tracking changes to data that is submitted to your form can be a crucial aspect of your form management. To detect changes to your provided form, the onFormDataChange function is available for working with forms. You can use this function to detect unsaved changes.

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How onFormDataChange works

The onFormDataChange function is used to track changes to form data. This can include changes to input or text fields, drop-down menus, checkboxes, and other form components that require user interaction. When form data changes, the onFormDataChange function is called to allow custom code to be executed. For example, if you have a Save button to save form data, you can disable it if the data on the form is the same as it was originally.

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Example workflow

The following provides an example that showcases how the onFormDataChange functionality is used to track changes.

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Form configuration

Define the logic for the onFormDataChange function and define input fields, dropdown lists, or other form components that require interactions from users. The following snippet provides an example of implemented onFormDataChange and a simple form in JSON format: 
  formEngineRsuiteCssLoader,
  ltrCssLoader,
  RsLocalizationWrapper,
  rSuiteComponents,
  rtlCssLoader,
} from '@react-form-builder/components-rsuite'

// Here you can pass the metadata of your components
const componentsMetadata = rSuiteComponents.map(
  (definer) => definer.build().model,
)

const view = createView(componentsMetadata)
  // The following parameters are required for correct CSS loading in LTR and RTL modes
  .withViewerWrapper(RsLocalizationWrapper)
  .withCssLoader(BiDi.LTR, ltrCssLoader)
  .withCssLoader(BiDi.RTL, rtlCssLoader)
  .withCssLoader('common', formEngineRsuiteCssLoader)

// Example form, in JSON format
const emptyForm = `
{
  "version": "1",
  "form": {
    "key": "Screen",
    "type": "Screen",
    "props": {},
    "children": [
      {
        "key": "firstName",
        "type": "RsInput",
        "props": {
          "label": {
            "value": "First name"
          }
        }
      },
      {
        "key": "lastName",
        "type": "RsInput",
        "props": {
          "label": {
            "value": "Last Name"
          }
        }
      },
      {
        "key": "rsButton1",
        "type": "RsButton",
        "props": {
          "appearance": {
            "value": "primary"
          },
          "children": {
            "value": "Save"
          },
          "color": {
            "value": "blue"
          },
          "disabled": {
            "value": false,
            "computeType": "function",
            "fnSource": "  return form.state.dataChanged !== true;"
          }
        }
      }
    ]
  },
  "localization": {},
  "languages": [
    {
      "code": "en",
      "dialect": "US",
      "name": "English",
      "description": "American English",
      "bidi": "ltr"
    }
  ],
  "defaultLanguage": "en-US"
}
`

const formName = 'Example'

async function getFormFn(name?: string) {
  if (name === formName) return emptyForm
  throw new Error(`Form '${name}' is not found.`)
}

const initialData = {
  firstName: 'Mars',
  lastName: 'Jupiter',
}

const App = () => {
  return (
    <FormViewer
      view={view}
      getForm={getFormFn}
      formName={formName}
      initialData={initialData}
      onFormDataChange={({data, state}) => {
        const sourceData = JSON.stringify(initialData)
        const currentData = JSON.stringify(data)
        state.dataChanged = sourceData !== currentData
      }}
    />
  )
}

export default App
Here, initial form data is defined within initialData. The onFormDataChange function compares initial data with the current form data (i.e., data). Both initial data and current data are stringified to facilitate the comparison process. The comparison results are saved within a user defined key-value observable storage called state. Learn more about the state storage by using the API-reference and the article in FAQ.

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Previewing form

Once your form is configured and the logic for onFormDataChange is defined, you can preview the form and the workflow by using the corresponding Preview button. The example form includes the Save button component with the functional Disabled property that switches on and off depending on the user data state: Functional_disable Therefore, in case the current provided data equals to the initial stored data, the Save button will be disabled. Consequently, users will be able to track changes and save the input only if changes and updates are provided.

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Next steps

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Official resources

Last modified on April 16, 2026