1 files changed, 40 insertions, 0 deletions
diff --git a/tools/eslint/lib/rules/valid-typeof.js b/tools/eslint/lib/rules/valid-typeof.js
new file mode 100644
index 0000000000..a108ab360f
--- /dev/null
+++ b/tools/eslint/lib/rules/valid-typeof.js
@@ -0,0 +1,40 @@
+/**
+ * @fileoverview Ensures that the results of typeof are compared against a valid string
+ * @author Ian Christian Myers
+ */
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    var VALID_TYPES = ["symbol", "undefined", "object", "boolean", "number", "string", "function"],
+        OPERATORS = ["==", "===", "!=", "!=="];
+
+    //--------------------------------------------------------------------------
+    // Public
+    //--------------------------------------------------------------------------
+
+    return {
+
+        "UnaryExpression": function (node) {
+            var parent, sibling;
+
+            if (node.operator === "typeof") {
+                parent = context.getAncestors().pop();
+
+                if (parent.type === "BinaryExpression" && OPERATORS.indexOf(parent.operator) !== -1) {
+                    sibling = parent.left === node ? parent.right : parent.left;
+
+                    if (sibling.type === "Literal" && VALID_TYPES.indexOf(sibling.value) === -1) {
+                        context.report(sibling, "Invalid typeof comparison value");
+                    }
+                }
+            }
+        }
+
+    };
+
+};