[core] Fix ReferenceError in browser builds without process polyfill

packages/material-ui/src/Button/Button.js

@@ -7,7 +7,7 @@ import warning from 'warning';
 import withStyles from '../styles/withStyles';
 import { fade } from '../styles/colorManipulator';
 import ButtonBase from '../ButtonBase';
-import { capitalize } from '../utils/helpers';
+import { capitalize, getEnv } from '../utils/helpers';
 
 export const styles = theme => ({
   /* Styles applied to the root element. */
@@ -227,13 +227,13 @@ function Button(props) {
   } = props;
 
   warning(
-    process.env.MUI_SUPPRESS_DEPRECATION_WARNINGS || variant !== 'flat',
+    getEnv('MUI_SUPPRESS_DEPRECATION_WARNINGS') || variant !== 'flat',
     'Material-UI: The `flat` Button variant will be removed in ' +
       'the next major release. `text` is equivalent and should be used instead.',
   );
 
   warning(
-    process.env.MUI_SUPPRESS_DEPRECATION_WARNINGS || variant !== 'raised',
+    getEnv('MUI_SUPPRESS_DEPRECATION_WARNINGS') || variant !== 'raised',
     'Material-UI: The `raised` Button variant will be removed in ' +
       'the next major release. `contained` is equivalent and should be used instead.',
   );

packages/material-ui/src/styles/createTypography.js

@@ -1,6 +1,7 @@
 import deepmerge from 'deepmerge'; // < 1kb payload overhead when lodash/merge is > 3kb.
 import warning from 'warning';
 import typographyMigration from './typographyMigration';
+import { getEnv } from '../utils/helpers';
 
 function round(value) {
   return Math.round(value * 1e5) / 1e5;
@@ -27,7 +28,7 @@ export default function createTypography(palette, typography) {
     // Tell Material-UI what's the font-size on the html element.
     // 16px is the default font-size used by browsers.
     htmlFontSize = 16,
-    suppressDeprecationWarnings = process.env.MUI_SUPPRESS_DEPRECATION_WARNINGS,
+    suppressDeprecationWarnings = getEnv('MUI_SUPPRESS_DEPRECATION_WARNINGS'),
     useNextVariants = false,
     // Apply the CSS properties to all the variants.
     allVariants,

packages/material-ui/src/utils/helpers.d.ts

@@ -3,5 +3,6 @@ export function contains<O1 extends O2, O2>(obj: O1, pred: O2): boolean;
 export function findIndex(arr: any[], pred: any): number;
 export function find<T>(arr: T[], pred: any): T;
 export function createChainedFunction(...funcs: ChainedFunction[]): (...args: any[]) => never;
+export function getEnv(name: string): any;
 
 export type ChainedFunction = ((...args: any[]) => void) | undefined | null;

packages/material-ui/src/utils/helpers.js

@@ -64,3 +64,10 @@ export function createChainedFunction(...funcs) {
     () => {},
   );
 }
+
+/**
+ * guarded getter for process.env.*
+ */
+export function getEnv(name) {
+  return typeof process !== 'undefined' && process.env ? process.env[name] : undefined;
+}

packages/material-ui/src/utils/helpers.test.js

@@ -1,5 +1,5 @@
 import { assert } from 'chai';
-import { capitalize, contains, find } from './helpers';
+import { capitalize, contains, find, getEnv } from './helpers';
 
 describe('utils/helpers.js', () => {
   describe('capitalize', () => {
@@ -33,4 +33,27 @@ describe('utils/helpers.js', () => {
       assert.strictEqual(contains(obj, failPred), false);
     });
   });
+
+  describe('getEnv', () => {
+    it('returns variables defined in process.env', () => {
+      assert.strictEqual(getEnv('NODE_ENV'), process.env.NODE_ENV);
+    });
+
+    describe('in browser', () => {
+      let oldEnv;
+
+      beforeEach(() => {
+        oldEnv = process.env;
+        process.env = undefined;
+      });
+
+      afterEach(() => {
+        process.env = oldEnv;
+      });
+
+      it('does not crash with an undefined process.env', () => {
+        assert.strictEqual(getEnv('NODE_ENV'), undefined);
+      });
+    });
+  });
 });