Issue #149: _.keys should throw a TypeError for non-objects.

test/objects.js

@@ -2,8 +2,33 @@ $(document).ready(function() {
 
   module("Object functions (values, extend, isEqual, and so on...)");
 
+  function raises(block, expected, message) {
+    var pass = typeof block == 'function',
+    isRegExp = expected && Object.prototype.toString.call(expected) == '[object RegExp]',
+    isFunction = !isRegExp && typeof expected == 'function';
+    if (!isFunction && !isRegExp && message == null) {
+      message = expected;
+      expected = null;
+    }
+    if (pass) {
+      try {
+        block();
+        pass = false;
+      } catch (error) {
+        pass = expected == null || (isRegExp && expected.test(error)) || (isFunction && expected.call(null, error));
+      }
+    }
+    ok(pass, typeof message == 'string' && message || 'error');
+  }
+
   test("objects: keys", function() {
+    var exception = /TypeError/;
     equals(_.keys({one : 1, two : 2}).join(', '), 'one, two', 'can extract the keys from an object');
+    raises(function() { _.keys(null); }, exception, 'throws an error for `null` values');
+    raises(function() { _.keys(void 0); }, exception, 'throws an error for `undefined` values');
+    raises(function() { _.keys(1); }, exception, 'throws an error for number primitives');
+    raises(function() { _.keys('a'); }, exception, 'throws an error for string primitives');
+    raises(function() { _.keys(true); }, exception, 'throws an error for boolean primitives');
   });
 
   test("objects: values", function() {

underscore.js

@@ -504,6 +504,7 @@
   // Retrieve the names of an object's properties.
   // Delegates to **ECMAScript 5**'s native `Object.keys`
   _.keys = nativeKeys || function(obj) {
+    if (obj !== Object(obj)) throw new TypeError('Invalid object');
     var keys = [];
     for (var key in obj) if (hasOwnProperty.call(obj, key)) keys[keys.length] = key;
     return keys;