Truncate decimal number (as strings) to a fixed number of places

Question

I want to truncate numbers (given as strings) to a fixed number of decimal places. The numbers can be negative (with a minus sign), positive (no sign). I'd prefer to round the numbers properly and keep trailing zeroes. I want the same number of decimal places, no matter how long the whole number is. The numbers will be stored back as strings.

For example:

140.234234234 -> 140.234
1.123123 -> 1.123
-12.789789 -> -12.790

Answer 1

First parse them as floats, then format with toFixed:

var nums = [
    "140.234234234", // -> 140.234
    "1.123123", // -> 1.123
    "-12.789789" // -> -12.790
];

nums.forEach(function(n) {
    console.log(parseFloat(n).toFixed(3));
});

http://codepen.io/anon/pen/IvxmA