Prevent a crash when working with symbols

demo/src/js/DemoApp.jsx

@@ -109,6 +109,9 @@ class DemoApp extends React.Component {
             <Button onClick={this.props.addFunction} style={styles.button}>
               Add Function
             </Button>
+            <Button onClick={this.props.addSymbol} style={styles.button}>
+              Add Symbol
+            </Button>
           </div>
         </div>
         <div style={styles.links}>
@@ -155,6 +158,7 @@ export default connect(
       type: 'HUGE_PAYLOAD',
       payload: Array.from({ length: 10000 }).map((_, i) => i)
     }),
-    addFunction: () => ({ type: 'ADD_FUNCTION' })
+    addFunction: () => ({ type: 'ADD_FUNCTION' }),
+    addSymbol: () => ({ type: 'ADD_SYMBOL' })
   }
 )(DemoApp);

demo/src/js/reducers.js

@@ -90,5 +90,7 @@ export default combineReducers({
       str => str + '!'
     ) : state,
   addFunction: (state=null, action) => action.type === 'ADD_FUNCTION' ?
-    { f: FUNC } : state
+    { f: FUNC } : state,
+  addSymbol: (state=null, action) => action.type === 'ADD_SYMBOL' ?
+    { s: Symbol('symbol') } : state
 });

src/ActionPreview.jsx

@@ -30,6 +30,8 @@ function getItemString(createTheme, type, data) {
       return 'fn';
     } else if (typeof val === 'string') {
       return `"${val.substr(0, 10) + (val.length > 10 ? '…' : '')}"`
+    } else if (typeof val === 'symbol') {
+      return 'symbol'
     } else {
       return val;
     }

src/JSONDiff.jsx

@@ -1,7 +1,7 @@
 import React from 'react';
 import JSONTree from '@alexkuz/react-json-tree';
 import themeable from './themeable';
-import stringify from 'javascript-stringify';
+import { stringify } from 'jsan';
 
 function stringifyAndShrink(val) {
   const str = stringify(val);