support DOMException via iserror from npm

Author: Thomas Grainger

package.json

@@ -14,6 +14,7 @@
   },
   "main": "src/singleton.js",
   "dependencies": {
+    "iserror": "^0.0.2",
     "json-stringify-safe": "^5.0.1"
   },
   "devDependencies": {

src/utils.js

@@ -1,19 +1,11 @@
 'use strict';
 
+var isError = require('iserror');
+
 function isObject(what) {
     return typeof what === 'object' && what !== null;
 }
 
-// Sorta yanked from https://github.com/joyent/node/blob/aa3b4b4/lib/util.js#L560
-// with some tiny modifications
-function isError(what) {
-    var toString = {}.toString.call(what);
-    return isObject(what) &&
-        toString === '[object Error]' ||
-        toString === '[object Exception]' || // Firefox NS_ERROR_FAILURE Exceptions
-        what instanceof Error;
-}
-
 module.exports = {
     isObject: isObject,
     isError: isError