javascript rounding function

Question

I want to write a function that given a number will set all but the first digit to zero and will increase the first digit by one

for example, 175 should become 200, 23 should become 30, etc. What is the best way to do this?

Answer 1

function truncUp(num) {
    var factor = Math.pow(10, (num+'').toString().length - 1);
    return Math.floor(num / factor) * factor + factor;
}

that was fun :D

And for the unnamed "others":

function truncUp(num) {
    num = Math.floor(num);
    var factor = Math.pow(10, (Math.abs(num)+'').toString().length - 1);
    return Math.floor(num / factor) * factor + ((Math.abs(num) - num == 0?1:2)*factor);
}

Answer 2

function myRound(num)
{
    var digits = String(num).length - 1,
        pow = Math.pow(10, digits);
    num /= pow;
    num = Math.ceil(num);
    num *= pow;
    return num;
}

Short version:

function myRound(num)
{
    var pow = Math.pow(10, String(num).length - 1);
    return Math.ceil(num/pow)*pow;
}

Tests:

> myRound(175)
  200
> myRound(23)
  30
> myRound(95)
  100