How "this" in methods of Javascript Number objects be converted to the numeric value of the object?
<p>It seems in Number objects, numeric values can be referenced directly using "this" instead of  this.valueOf() or something like "this.value", for example:  </p>

<pre><code>Number.prototype.printPlusOne=function(){ 
      var tmp=this+1;
      alert(tmp); 
}
var n=new Number("5");
n.printPlusOne();  
</code></pre>

<p>And why is this possible(using "this" directly instead of "this.valueOf()" in the addition above)?<br>
I didn't find this feature in the Number specification, Did I missed something?<br>
And further more, Is this automatic conversion feature used in other classes of objects?</p>
