Javascript: formatting a rounded number to N decimals

I found a way. This is Christoph's code with a fix:

function toFixed(value, precision) {
    var precision = precision || 0,
        power = Math.pow(10, precision),
        absValue = Math.abs(Math.round(value * power)),
        result = (value < 0 ? '-' : '') + String(Math.floor(absValue / power));

    if (precision > 0) {
        var fraction = String(absValue % power),
            padding = new Array(Math.max(precision - fraction.length, 0) + 1).join('0');
        result += '.' + padding + fraction;
    }
    return result;
}

Read the details of repeating a character using an array constructor here if you are curious as to why I added the "+ 1".

I think that there is a more simple approach to all given here, and is the method Number.toFixed() already implemented in JavaScript.

simply write:

var myNumber = 2;

myNumber.toFixed(2); //returns "2.00"
myNumber.toFixed(1); //returns "2.0"

etc...

That's not a rounding ploblem, that is a display problem. A number doesn't contain information about significant digits; the value 2 is the same as 2.0000000000000. It's when you turn the rounded value into a string that you have make it display a certain number of digits.

You could just add zeroes after the number, something like:

var s = number.toString();
if (s.indexOf('.') == -1) s += '.';
while (s.length < s.indexOf('.') + 4) s += '0';

(Note that this assumes that the regional settings of the client uses period as decimal separator, the code needs some more work to function for other settings.)