Add support for useTheme hook

CHANGELOG.md

@@ -6,6 +6,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Next
 
 - Improve bundle size ([#83](https://github.com/cssinjs/theming/pull/83))
+- Add useTheme hook ([#84](https://github.com/cssinjs/theming/pull/84))
 
 ### 3.0.3 (2019-1-20)
 

package.json

@@ -74,8 +74,8 @@
     "eslint-config-jss": "^5.0.1",
     "flow-bin": "^0.88.0",
     "nyc": "^13.1.0",
-    "react": "^16.6.0",
-    "react-test-renderer": "^16.6.0",
+    "react": "^16.8.0",
+    "react-test-renderer": "^16.8.0",
     "rimraf": "^2.6.1",
     "rollup": "^0.66.6",
     "rollup-plugin-babel": "^4.0.3",

src/create-use-theme.js

@@ -0,0 +1,15 @@
+// @flow
+
+import React, { type Context } from 'react';
+import warning from 'tiny-warning';
+import isObject from './is-object';
+
+export default function createUseTheme<Theme>(context: Context<Theme>) {
+  return () => {
+    const theme = React.useContext(context);
+
+    warning(isObject(theme), '[theming] Please use useTheme only with the ThemeProvider');
+
+    return theme;
+  };
+}

src/index.js

@@ -4,6 +4,7 @@ import { createContext, type Context } from 'react';
 
 import createThemeProvider, { type ThemeProviderProps } from './create-theme-provider';
 import createWithTheme from './create-with-theme';
+import createUseTheme from './create-use-theme';
 
 type ExtractReturnType<Theme> = <ReturnType>(
   (context: Context<Theme>) => ReturnType
@@ -21,6 +22,7 @@ function createTheming<Theme>(context: Context<Theme>): Theming<Theme> {
   return {
     context,
     withTheme: createWithTheme(context),
+    useTheme: createUseTheme(context),
     ThemeProvider: createThemeProvider(context),
   };
 }

src/index.test.js

@@ -20,7 +20,7 @@ test('createTheming()\'s key names', (t) => {
   const context = createContext({});
   const theming = createTheming(context);
   const actual = Object.keys(theming);
-  const expected = ['context', 'withTheme', 'ThemeProvider'];
+  const expected = ['context', 'withTheme', 'useTheme', 'ThemeProvider'];
 
   t.deepEqual(
     actual,