You can do
parseFloat(2.5).toFixed(4);
If you need exactly the same floating point you may have to figure out the amount
var string = '2.54355';
parseFloat(string).toFixed(string.split('.')[1].length);
But i don't really understand why you even need to use parseFloat then? Numbers in javascript do not retain the floating-point count. so you would have to keep them as strings, and calculate against them as floats.
