Question

I would love to be able to move a decimal point 2 places across an unknown amount of numbers without using math. I know that seems weird, but finite precision causes some shifts. My javascript is not strong, but I’d really like to learn how to chop up a number and do this if it’s possible. So, I’m hoping you awesome folks can help.

The problem:

• 575/960 = 0.5989583333333334 using the console
• I would like to make that a copy and pastable percentage like: 59.89583333333334%
• If I use math and multiply by 100, it returns 59.895833333333336 because of finite precision

Is there a way to make that a string and just always move the decimal 2 places to the right to skip the math?

Here’s a fiddle too, with the codes: http://jsfiddle.net/dandenney/W9fXz/

If you want to know why I need it and want the precision, it’s for this little tool that I made for getting responsive percentages without using the calculator: http://responsv.com/flexible-math

Answer 1

If the original number is of this type of known structure and always has at least two digits to the right of the decimal, you can do it like this:

function makePercentStr(num) {
    var numStr = num + "";
    // if no decimal point, add .00 on end
    if (numStr.indexOf(".") == -1) {
        numStr += ".00";
    } else {
        // make sure there's at least two chars after decimal point
        while (!numStr.match(/\.../)) {
            numStr += "0";        
        }
    }
    return(numStr.replace(/\.(..)/, "$1.")
           .replace(/^0+/, "")    // trim leading zeroes
           .replace(/\.$/, "")    // trim trailing decimals
           .replace(/^$/, "0")    // if empty, add back a single 0
           + "%");
}

Working demo with test cases: http://jsfiddle.net/jfriend00/ZRNuw/