Question

Can you round a number in JavaScript to one character after the decimal point (properly rounded)?

I tried the *10, round, /10, but it leaves two decimals at the end of the int.

Answer 1

Math.round(num * 10) / 10 works, and here is an example…

var number = 12.3456789
var rounded = Math.round(number * 10) / 10
// rounded is 12.3

If you want it to have one decimal place, even when that would be a 0, then add…

var fixed = rounded.toFixed(1)
// 'fixed' is always to one decimal point
// NOTE: .toFixed() returns a string!

// To convert back to number format
parseFloat(number.toFixed(2))
// 12.34
// but that will not retain any trailing zeros

// So, just make sure it is the last step before output,
// and use a number format during calculations!

Using this principle, for reference, here is a handy little round function that takes precision…

function round(value, precision) {
    var multiplier = Math.pow(10, precision || 0);
    return Math.round(value * multiplier) / multiplier;
}

… usage …

round(12345.6789, 2) // 12345.68
round(12345.6789, 1) // 12345.7

… defaults to round to nearest whole number (precision 0) …

round(12345.6789) // 12346

… and can be used to round to nearest 10 or 100, etc…

round(12345.6789, -1) // 12350
round(12345.6789, -2) // 12300

… and correct handling of negative numbers …

round(-123.45, 1) // -123.4
round(123.45, 1) // 123.5

… and can be combined with toFixed to format consistently as string …

round(456.7, 2).toFixed(2) // "456.70"