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

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Errors thrown from different contexts (such as an iframe or webworker) are 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

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,
@@ -673,6 +674,24 @@ 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

@@ -1880,6 +1880,43 @@ 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) {