How "this" in methods of Javascript Number objects be converted to the numeric value of the object? -

How "this" in methods of Javascript Number objects be converted to the numeric value of the object? -

it seems in number objects, numeric values can referenced straight using "this" instead of this.valueof() or "this.value", example:

number.prototype.printplusone=function(){ var tmp=this+1; alert(tmp); } var n=new number("5"); n.printplusone();

and why possible(using "this" straight instead of "this.valueof()" in add-on above)? didn't find feature in number specification, did missed something? , farther more, automatic conversion feature used in other classes of objects?

neither operand of + operator string, javascript calls valueof implicitly convert object (a number, in case) primitive value, in order perform numeric addition. quoting david flanagan:

if object has valueof() method returns primitive value, javascript converts (if necessary) primitive value number , returns result.

so, this implicitly converted primitive value.

if did silly override number.valueof:

number.prototype.valueof = function() { homecoming 10; }

then function alert 11 instead.

javascript