How to Round Numbers to One Decimal Place in JavaScript?

How to Round a Number to One Decimal Place in JavaScript

In JavaScript, you can round a number to one character after the decimal point using the following approach:

var num = 12.3456789;
var rounded = Math.round(num * 10) / 10;
console.log(rounded); // Output: 12.3

This works by multiplying the number by 10, rounding the result, and then dividing by 10 again. This ensures that only one decimal place is retained.

To round a number to one decimal place, even when that would be a 0, you can use .toFixed() as follows:

var rounded = num.toFixed(1);
console.log(rounded); // Output: "12.3"

Note that .toFixed() returns a string, so you may need to convert it back to a number if necessary.

For added flexibility, you can create a custom round() function that takes a precision argument:

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

This function can be used as follows:

round(12345.6789, 2); // Output: 12345.68
round(12345.6789, 1); // Output: 12345.7
round(12345.6789); // Output: 12346
round(-123.45, 1); // Output: -123.4

The precision argument defaults to 0, which rounds the number to the nearest whole number.

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