# JS: Format Number

By Xah Lee. Date: . Last updated: .

JavaScript does not have a βformatβ or βprintfβ function. The following code are solutions.

## Show Only N Decimal Places

Use `toFixed`.

## Show Only N Significant Digits

Use `toPrecision`, but result may be in exponential notation.

## Show in Exponential Notation

Use `toExponential`

Example output: ` "3.12e+2"`

## Format Number with Metric Prefix

```const xah_format_number = ((n, m = 1) => {
/*
format number with metric prefix, e.g. 1.2 k
n is integer. The number to be converted
m is integer. The number of decimal places to show. Default to 1.
returns a string, with possibly one of k M G T ... suffix.

http://xahlee.info/js/js_format_number.html
version 2019-04-15
*/
const prefix = [
"",
" k",
" M",
" G",
" T",
" P",
" E",
" Z",
" Y",
" * 10^27",
" * 10^30",
" * 10^33",
]; // should be enough. Number.MAX_VALUE is about 10^308
let ii = 0;
while ((n = n / 1000) >= 1) ii++;
return (n * 1000).toFixed(m) + prefix[ii];
});

/* test--------------------------------------------------- */

console.log(
xah_format_number(111, 1) === "111.0",
xah_format_number(111222, 1) === "111.2 k",
xah_format_number(111222333, 1) === "111.2 M",
xah_format_number(111222333444, 1) === "111.2 G",
xah_format_number(111222333444) === "111.2 G",
xah_format_number(111222333444, 3) === "111.222 G",
xah_format_number(111222333444, 0) === "111 G",
);```