fix(*): correctly detect Error instances from different contexts

Previously, errors thrown from different contexts (such as an iframe or
webworker) were not detected as `Error` instances and handled accordingly.
This commit fixes it by introducing an `isError()` helper, that is able to
correctly detect such instances.

Fixes #15868

Closes #15872

Author: Thomas Grainger

src/.eslintrc.json

@@ -50,6 +50,7 @@
     "isNumber": false,
     "isNumberNaN": false,
     "isDate": false,
+    "isError": false,
     "isArray": false,
     "isFunction": false,
     "isRegExp": false,

src/Angular.js

@@ -45,6 +45,7 @@
   isNumber,
   isNumberNaN,
   isDate,
+  isError,
   isArray,
   isFunction,
   isRegExp,
@@ -629,6 +630,24 @@ function isDate(value) {
  */
 var isArray = Array.isArray;
 
+/**
+ * @description
+ * Determines if a reference is an `Error`.
+ * Loosely based on https://www.npmjs.com/package/iserror
+ *
+ * @param {*} value Reference to check.
+ * @returns {boolean} True if `value` is an `Error`.
+ */
+function isError(value) {
+  var tag = toString.call(value);
+  switch (tag) {
+    case '[object Error]': return true;
+    case '[object Exception]': return true;
+    case '[object DOMException]': return true;
+    default: return value instanceof Error;
+  }
+}
+
 /**
  * @ngdoc function
  * @name angular.isFunction

src/ng/compile.js

@@ -3098,7 +3098,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
           }
           linkQueue = null;
         }).catch(function(error) {
-          if (error instanceof Error) {
+          if (isError(error)) {
             $exceptionHandler(error);
           }
         });

src/ng/log.js

@@ -132,7 +132,7 @@ function $LogProvider() {
     };
 
     function formatError(arg) {
-      if (arg instanceof Error) {
+      if (isError(arg)) {
         if (arg.stack && formatStackTrace) {
           arg = (arg.message && arg.stack.indexOf(arg.message) === -1)
               ? 'Error: ' + arg.message + '\n' + arg.stack

src/ng/q.js

@@ -381,7 +381,7 @@ function qFactory(nextTick, exceptionHandler, errorOnUnhandledRejections) {
       if (!toCheck.pur) {
         toCheck.pur = true;
         var errorMessage = 'Possibly unhandled rejection: ' + toDebugString(toCheck.value);
-        if (toCheck.value instanceof Error) {
+        if (isError(toCheck.value)) {
           exceptionHandler(toCheck.value, errorMessage);
         } else {
           exceptionHandler(errorMessage);

test/.eslintrc.json

@@ -64,6 +64,7 @@
     "isNumber": false,
     "isNumberNaN": false,
     "isDate": false,
+    "isError": false,
     "isArray": false,
     "isFunction": false,
     "isRegExp": false,

test/AngularSpec.js

@@ -1855,6 +1855,43 @@ describe('angular', function() {
     });
   });
 
+  describe('isError', function() {
+    function testErrorFromDifferentContext(createError) {
+      var iframe = document.createElement('iframe');
+      document.body.appendChild(iframe);
+      try {
+        var error = createError(iframe.contentWindow);
+        expect(isError(error)).toBe(true);
+      } finally {
+        iframe.parentElement.removeChild(iframe);
+      }
+    }
+
+    it('should not assume objects are errors', function() {
+      var fakeError = { message: 'A fake error', stack: 'no stack here'};
+      expect(isError(fakeError)).toBe(false);
+    });
+
+    it('should detect simple error instances', function() {
+      expect(isError(new Error())).toBe(true);
+    });
+
+    it('should detect errors from another context', function() {
+      testErrorFromDifferentContext(function(win) {
+        return new win.Error();
+      });
+    });
+
+    it('should detect DOMException errors from another context', function() {
+      testErrorFromDifferentContext(function(win) {
+        try {
+          win.document.querySelectorAll('');
+        } catch (e) {
+          return e;
+        }
+      });
+    });
+  });
 
   describe('isRegExp', function() {
     it('should return true for RegExp object', function() {

test/ng/qSpec.js

@@ -37,7 +37,7 @@ describe('q', function() {
   // The following private functions are used to help with logging for testing invocation of the
   // promise callbacks.
   function _argToString(arg) {
-    return (typeof arg === 'object' && !(arg instanceof Error)) ? toJson(arg) : '' + arg;
+    return (typeof arg === 'object' && !(isError(arg))) ? toJson(arg) : '' + arg;
   }
 
   function _argumentsToString(args) {