diff --git a/lib/browser.js b/lib/browser.js
index 60dbbb99..8f9be9b3 100644
--- a/lib/browser.js
+++ b/lib/browser.js
@@ -10,7 +10,7 @@
     options.bare = true;
     return Function(CoffeeScript.compile(code, options))();
   };
-  if (!(typeof window !== "undefined" && window !== null)) {
+  if (typeof window == "undefined" || window === null) {
     return;
   }
   CoffeeScript.load = function(url, options) {
diff --git a/lib/nodes.js b/lib/nodes.js
index 4a09f7df..2396f52c 100644
--- a/lib/nodes.js
+++ b/lib/nodes.js
@@ -1459,10 +1459,21 @@
     })();
     __extends(Existence, Base);
     Existence.prototype.children = ['expression'];
+    Existence.prototype.invert = function() {
+      this.negated = !this.negated;
+      return this;
+    };
     Existence.prototype.compileNode = function(o) {
-      var code;
+      var code, sym;
       code = this.expression.compile(o);
-      code = IDENTIFIER.test(code) && !o.scope.check(code) ? "typeof " + code + " !== \"undefined\" && " + code + " !== null" : "" + code + " != null";
+      code = (function() {
+        if (IDENTIFIER.test(code) && !o.scope.check(code)) {
+          return this.negated ? "typeof " + code + " == \"undefined\" || " + code + " === null" : "typeof " + code + " != \"undefined\" && " + code + " !== null";
+        } else {
+          sym = this.negated ? '==' : '!=';
+          return "" + code + " " + sym + " null";
+        }
+      }).call(this);
       return o.level <= LEVEL_COND ? code : "(" + code + ")";
     };
     return Existence;
diff --git a/src/nodes.coffee b/src/nodes.coffee
index 0d160069..cd09b4a4 100644
--- a/src/nodes.coffee
+++ b/src/nodes.coffee
@@ -1214,12 +1214,20 @@ exports.Existence = class Existence extends Base
 
   constructor: (@expression) ->
 
+  invert: ->
+    @negated = not @negated
+    this
+
   compileNode: (o) ->
     code = @expression.compile o
     code = if IDENTIFIER.test(code) and not o.scope.check code
-      "typeof #{code} !== \"undefined\" && #{code} !== null"
+      if @negated
+        "typeof #{code} == \"undefined\" || #{code} === null"
+      else
+        "typeof #{code} != \"undefined\" && #{code} !== null"
     else
-      "#{code} != null"
+      sym = if @negated then '==' else '!='
+      "#{code} #{sym} null"
     if o.level <= LEVEL_COND then code else "(#{code})"
 
 #### Parens