Trouble with javascript subtraction

I'm working on a simple subtraction problem, but unfortunately it keeps returning NaN

Here is the function

   function subtraction(a, b) {
        var regexp = /[$][,]/g;

        a = a.replace(regexp, "");
        b = b.replace(regexp, "");


        var _a = parseFloat(a);
        var _b = parseFloat(b);

        return _a - _b;
     }

And here is how I'm calling it.

txtGoodWill.value = subtraction(txtSellingPrice.value, txtBalanceSheet.value);

The numbers that get submitted to 开发者_如何学JAVAthe function are ONLY Currency (IE: $2,000 or $20, etc)

Now I know that I cannot subtract numbers with a $ or a ,, but I can't for the life of me figure out why they are getting evaluated in the equasion.

Your regular expression only matches if a $ is directly followed by ,. Use /[$,]/g instead to match all occurrences of either of the two characters.

I think you want var regexp = /[$,]/g; (both the $ and , inside the same set of square brackets).