AS3 adding 1 (+1) not working on string cast to Number?

just learning as3 for flex. i am trying to do this:

var someNumber:String = "10150125903517628"; //this开发者_如何学运维 is the actual number i noticed the issue with

var result:String = String(Number(someNumber) + 1);

I've tried different ways of putting the expression together and no matter what i seem to do the result is always equal to 10150125903517628 rather than 10150125903517629

Anyone have any ideas??! thanks!

All numbers in JavaScript/ActionScript are effectively double-precision IEEE-754 floats. These use a 64-bit binary number to represent your decimal, and have a precision of roughly 16 or 17 decimal digits.

You've run up against the limit of that format with your 17-digit number. The internal binary representation of 10150125903517628 is no different to that of 10150125903517629 which is why you're not seeing any difference when you add 1.

If, however, you add 2 then you will (should?) see the result as 10150125903517630 because that's enough of a "step" that the internal binary representation will change.