Provide FormValues for createDecorator (#39)

If FormValues is specified for a form, then type 'Decorator<object>' is not assignable to type 'Decorator<FormValues>'

Author: A11oW

package-lock.json

@@ -52,7 +52,7 @@
     "eslint-plugin-import": "^2.16.0",
     "eslint-plugin-jsx-a11y": "^6.2.1",
     "eslint-plugin-react": "^7.12.4",
-    "final-form": "^4.11.1",
+    "final-form": "^4.19.1",
     "flow": "^0.2.3",
     "flow-bin": "^0.92.1",
     "glow": "^1.2.2",

package.json

@@ -1,13 +1,13 @@
 // @flow
-import type { Decorator, FormApi } from 'final-form'
+import type { Decorator, FormApi, FormValuesShape } from 'final-form'
 import type { Calculation, Updates } from './types'
 import { getIn } from 'final-form'
 import isPromise from './isPromise'
 
 const tripleEquals = (a: any, b: any) => a === b
-const createDecorator = (...calculations: Calculation[]): Decorator => (
-  form: FormApi
-) => {
+const createDecorator = <FormValues: FormValuesShape>(
+  ...calculations: Calculation[]
+): Decorator<FormValues> => (form: FormApi<FormValues>) => {
   let previousValues = {}
   const unsubscribe = form.subscribe(
     ({ values }) => {

src/decorator.js

@@ -23,6 +23,6 @@ export type Calculation = {
   isEqual?: (a: any, b: any) => boolean,
 }
 
-export default function createDecorator(
+export default function createDecorator<FormValues = object>(
   ...calculations: Calculation[]
-): Decorator
+): Decorator<FormValues>

src/index.d.ts

@@ -1,7 +1,7 @@
 // @flow
-import type { Decorator } from 'final-form'
+import type { Decorator, FormValuesShape } from 'final-form'
 import type { Calculation } from './types'
 
-declare export default function createDecorator(
+declare export default function createDecorator<FormValues: FormValuesShape>(
   ...calculations: Calculation[]
-): Decorator
+): Decorator<FormValues>