Add modifiedSinceLastSubmit (#799)

Author: Pedro Lourenço

docs/types/FieldRenderProps.md

@@ -144,6 +144,18 @@ Optional: May not be present if you have not [subscribed](FieldProps#subscriptio
 
 Once `true`, it will remain `true` for the lifetime of the field, or until the form is reset.
 
+## `meta.modifiedSinceLastSubmit`
+
+```ts
+boolean
+```
+
+Optional: May not be present if you have not [subscribed](FieldProps#subscription) to `modifiedSinceLastSubmit`.
+
+`true` if this field's value has ever been changed since last submission. `false` otherwise.
+
+Once `true`, it will remain `true` until the next submit action, or until the form is reset.
+
 ## `meta.pristine`
 
 ```ts

src/getters.js

@@ -23,6 +23,7 @@ export const addLazyFormState = (dest: Object, state: FormState): void =>
     'initialValues',
     'invalid',
     'modified',
+    'modifiedSinceLastSubmit',
     'pristine',
     'submitError',
     'submitErrors',
@@ -47,6 +48,7 @@ export const addLazyFieldMetaState = (dest: Object, state: FieldState): void =>
     'invalid',
     'length',
     'modified',
+    'modifiedSinceLastSubmit',
     'pristine',
     'submitError',
     'submitFailed',

src/types.js.flow

@@ -39,6 +39,7 @@ export type FieldRenderProps = {
     invalid?: boolean,
     length?: number,
     modified?: boolean,
+    modifiedSinceLastSubmit?: boolean,
     pristine?: boolean,
     submitError?: any,
     submitFailed?: boolean,

src/useField.test.js

@@ -48,6 +48,7 @@ describe('useField', () => {
       expect(meta.invalid).toBe(false)
       expect(meta.length).toBeUndefined()
       expect(meta.modified).toBe(false)
+      expect(meta.modifiedSinceLastSubmit).toBe(false)
       expect(meta.pristine).toBe(true)
       expect(meta.submitError).toBeUndefined()
       expect(meta.submitFailed).toBe(false)