Ensure _.isError works with subclasses values. [closes #1994]

lodash.js

@@ -9761,8 +9761,11 @@
      * // => false
      */
     function isError(value) {
-      return isObjectLike(value) &&
-        typeof value.message == 'string' && objectToString.call(value) == errorTag;
+      if (!isObjectLike(value)) {
+        return false;
+      }
+      var Ctor = value.constructor;
+      return typeof Ctor == 'function' && objectToString.call(Ctor.prototype) == errorTag;
     }
 
     /**
@@ -13121,7 +13124,7 @@
       try {
         return apply(func, undefined, args);
       } catch (e) {
-        return isObject(e) ? e : new Error(e);
+        return isError(e) ? e : new Error(e);
       }
     });
 

test/test.js

@@ -352,6 +352,32 @@
   function(chr) { return /\s/.exec(chr); })
   .join('');
 
+  /**
+   * The custom error constructor.
+   *
+   * @private
+   * @param {string} message The error message.
+   * @returns {Object} Returns the new error object instance.
+   */
+  function CustomError(message) {
+    this.name = 'CustomError';
+    this.message = message;
+  }
+
+  CustomError.prototype = lodashStable.create(Error.prototype);
+
+  /**
+   * Removes all own enumerable properties from a given object.
+   *
+   * @private
+   * @param {Object} object The object to empty.
+   */
+  function emptyObject(object) {
+    lodashStable.forOwn(object, function(value, key, object) {
+      delete object[key];
+    });
+  }
+
   /**
    * Extracts the unwrapped value from its wrapper.
    *
@@ -375,18 +401,6 @@
     return result;
   }
 
-  /**
-   * Removes all own enumerable properties from a given object.
-   *
-   * @private
-   * @param {Object} object The object to empty.
-   */
-  function emptyObject(object) {
-    lodashStable.forOwn(object, function(value, key, object) {
-      delete object[key];
-    });
-  }
-
   /**
    * Sets a non-enumerable property value on `object`.
    *
@@ -1519,13 +1533,6 @@
     QUnit.test('should preserve custom errors', function(assert) {
       assert.expect(1);
 
-      function CustomError(message) {
-        this.name = 'CustomError';
-        this.message = message;
-      }
-
-      CustomError.prototype = lodashStable.create(Error.prototype);
-
       var actual = _.attempt(function() { throw new CustomError('x'); });
       assert.ok(actual instanceof CustomError);
     });
@@ -9219,6 +9226,12 @@
       assert.deepEqual(actual, expected);
     });
 
+    QUnit.test('should return `true` for subclassed values', function(assert) {
+      assert.expect(1);
+
+      assert.strictEqual(_.isError(new CustomError('x')), true);
+    });
+
     QUnit.test('should return `false` for non error objects', function(assert) {
       assert.expect(12);
 
@@ -11012,11 +11025,11 @@
 
   (function() {
     QUnit.test('should return `false` for subclassed values', function(assert) {
-      assert.expect(8);
+      assert.expect(7);
 
       var funcs = [
-        'isArray', 'isBoolean', 'isDate', 'isError',
-        'isFunction', 'isNumber', 'isRegExp', 'isString'
+        'isArray', 'isBoolean', 'isDate', 'isFunction',
+        'isNumber', 'isRegExp', 'isString'
       ];
 
       lodashStable.each(funcs, function(methodName) {