Merge branch 'master' of http://github.com/attaboy/wtfjs

posts/2010-06-16-typeof-number-is-not-number.md

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+How do you determine if a number is an integer in JavaScript?
+
+    x = 1;
+
+    x === Math.floor(x);
+    // returns true
+
+But what happens if we try to add a method for this to the Number prototype?
+
+    Number.prototype.isInteger = function() {
+      return this === Math.floor(this);
+    }
+
+    x = 1;
+
+    x.isInteger();
+    // returns false!
+
+Why? It turns out that when you add methods to Number, the type of the number inside the method becomes "object" rather than "number", but Math.floor returns a result of type "number". If you use the === operator, the two values are no longer equal because they're different types. So the method can be fixed two ways.
+
+Solution 1 is to avoid comparing types:
+
+    Number.prototype.isInteger = function() {
+      return this == Math.floor(this);
+      // works but breaks if you care about 0 vs other falsy values
+    }
+
+Solution 2 is better; cast "this" to the Number type and then the types are equal.
+
+    Number.prototype.isInteger = function() {
+      return Number(this) === Math.floor(this);
+    }
+
+--- [@attaboy](http://twitter.com/attaboy)