Consider null as defined. Closes #1

Author: curran

README.md

@@ -2,7 +2,9 @@
 
 [![NPM](https://nodei.co/npm/reactive-function.png)](https://npmjs.org/package/reactive-function)
 
-A library for managing data flows and changing state.
+ * A library for managing data flows graphs and changing state.
+ * Built on [reactive-property](https://github.com/curran/reactive-property).
+ * The foundation for [reactive-model](https://github.com/curran/reactive-model).
 
 # Usage
 
@@ -55,7 +57,7 @@ ReactiveFunction({
 });
 ```
 
-This defines a "reactive function" that will be invoked when its inputs (`firstName` and `lastName`) are both defined and whenever either one changes. The function will be invoked on the next tick of the JavaScript event loop after it is defined and after any dependencies change.
+This defines a "reactive function" that will be invoked when its inputs (`firstName` and `lastName`) are both defined and whenever either one changes ([`null` is considered a defined value](https://github.com/curran/reactive-function/issues/1)). The function will be invoked on the next tick of the JavaScript event loop after it is defined and after any dependencies change.
 
 To force a synchronous evaluation of all reactive functions whose dependencies have updated, you can call
 

index.js

@@ -128,9 +128,14 @@ function debounce(fn){
 
 // Returns true if all elements of the given array are defined.
 function defined(arr){
-  return !arr.some(function (d){
-    return typeof d === "undefined" || d === null;
-  });
+  return !arr.some(isUndefined);
+}
+
+// Returns true if the given object is undefined.
+// Returns false if the given object is some value, including null.
+// Inspired by http://ryanmorr.com/exploring-the-eternal-abyss-of-null-and-undefined/
+function isUndefined(obj){
+  return obj === void 0;
 }
 
 module.exports = ReactiveFunction;

test.js

@@ -271,7 +271,7 @@ describe("ReactiveFunction", function() {
     assert.equal(numInvocations, 0);
   });
 
-  it("Should not invoke if an input is null.", function (){
+  it("Should invoke if an input is null.", function (){
     var numInvocations = 0;
     var a = ReactiveProperty(null);
     var b = ReactiveProperty(10);
@@ -287,7 +287,7 @@ describe("ReactiveFunction", function() {
     });
 
     ReactiveFunction.digest();
-    assert.equal(numInvocations, 0);
+    assert.equal(numInvocations, 1);
   });
 
   it("Should be able to implement unidirectional data binding.", function (){