Add a leading zero to a single-digit number

gistfile1.js

// 12 => 12
// 1 => 01
number = ("0" + number).slice(-2);

// leading zeros ( good for score keepers? )
// (12,1) => 12,   (12,2) => 12,   (12,3) => 012
// (1,5) => 00001

function leadingZeros(number,howManyZeros) {
    var numStr = number.toString();
    for(var i = 1; i < howManyZeros; i++) {
        if(number < Math.pow(10,i)) {
            numStr = "0" + numStr;
        }
    }
    return numStr;
}