How to format numbers by prepending 0 to single-digit numbers?

Question

I want to format a number to have two digits. The problem is caused when 0–9 is passed, so I need it to be formatted to 00–09.

Is there a number formatter in JavaScript?

Answer 1

Edit (2021):

It's no longer necessary to format numbers by hand like this anymore. This answer was written way-back-when in the distant year of 2011 when IE was important and babel and bundlers were just a wonderful, hopeful dream.

I think it would be a mistake to delete this answer; however in case you find yourself here, I would like to kindly direct your attention to the second highest voted answer to this question as of this edit.

It will introduce you to the use of .toLocaleString() with the options parameter of {minimumIntegerDigits: 2}. Exciting stuff. Below I've recreated all three examples from my original answer using this method for your convenience.

[7, 7.5, -7.2345].forEach(myNumber => {
  let formattedNumber = myNumber.toLocaleString('en-US', {
    minimumIntegerDigits: 2,
    useGrouping: false
  })
  console.log(
    'Input:    ' + myNumber + '\n' +
    'Output:   ' + formattedNumber
  )
})

---

Original Answer:

The best method I've found is something like the following:

_{(Note that this simple version only works for positive integers)}

var myNumber = 7;
var formattedNumber = ("0" + myNumber).slice(-2);
console.log(formattedNumber);

For decimals, you could use this code (it's a bit sloppy though).

var myNumber = 7.5;
var dec = myNumber - Math.floor(myNumber);
myNumber = myNumber - dec;
var formattedNumber = ("0" + myNumber).slice(-2) + dec.toString().substr(1);
console.log(formattedNumber);

Lastly, if you're having to deal with the possibility of negative numbers, it's best to store the sign, apply the formatting to the absolute value of the number, and reapply the sign after the fact. Note that this method doesn't restrict the number to 2 total digits. Instead it only restricts the number to the left of the decimal (the integer part). (The line that determines the sign was found here).

var myNumber = -7.2345;
var sign = myNumber?myNumber<0?-1:1:0;
myNumber = myNumber * sign + ''; // poor man's absolute value
var dec = myNumber.match(/\.\d+$/);
var int = myNumber.match(/^[^\.]+/);

var formattedNumber = (sign < 0 ? '-' : '') + ("0" + int).slice(-2) + (dec !== null ? dec : '');
console.log(formattedNumber);

Answer 2

Use the toLocaleString() method in any number. So for the number 6, as seen below, you can get the desired results.

(6).toLocaleString('en-US', {minimumIntegerDigits: 2, useGrouping:false})

Will generate the string '06'.

Answer 3

If the number is higher than 9, convert the number to a string (consistency). Otherwise, add a zero.

function n(n){
    return n > 9 ? "" + n: "0" + n;
}

n( 9); //Returns "09"
n(10); //Returns "10"
n(999);//Returns "999"

Answer 4

Here's a simple number padding function that I use usually. It allows for any amount of padding.

function leftPad(number, targetLength) {
    var output = number + '';
    while (output.length < targetLength) {
        output = '0' + output;
    }
    return output;
}

Examples:

leftPad(1, 2) // 01
leftPad(10, 2) // 10
leftPad(100, 2) // 100
leftPad(1, 3) // 001
leftPad(1, 8) // 00000001

Answer 5

In all modern browsers you can use

numberStr.padStart(2, "0");

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart

function zeroPad(numberStr) {
  return numberStr.padStart(2, "0");
}

var numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

numbers.forEach(
  function(num) {
    var numString = num.toString();
    
    var paddedNum = zeroPad(numString);

    console.log(paddedNum);
  }
);

Answer 6

@Lifehack's answer was very useful to me; where I think we can do it in one line for positive numbers

 String(input).padStart(2, '0');

Answer 7

("0" + (date.getMonth() +　1)).slice(-2);
("0" + (date.getDay())).slice(-2);

Answer 8

You can do:

function pad2(number) {
   return (number < 10 ? '0' : '') + number
}

Example:

document.write(pad2(0) + '<br />');
document.write(pad2(1) + '<br />');
document.write(pad2(2) + '<br />');
document.write(pad2(10) + '<br />');
document.write(pad2(15) + '<br />');

Result:

00
01
02
10
15

Answer 9

It seems you might have a string, instead of a number. use this:

var num = document.getElementById('input').value,
    replacement = num.replace(/^(\d)$/, '0$1');
document.getElementById('input').value = replacement;

Here's an example: http://jsfiddle.net/xtgFp/

Answer 10

Here is a very simple solution that worked well for me.

First declare a variable to hold your number.

var number;

Now convert the number to a string and hold it in another variable;

var numberStr = number.toString();

Now you can test the length of this string , if it is less than desired you can append a 'zero' at the beginning.

if(numberStr.length < 2){
      number = '0' + number;
}

Now use the number as desired

console.log(number);

Answer 11

Quick and dirty one liner....

function zpad(n, len) {
  return 0..toFixed(len).slice(2,-n.toString().length)+n.toString();
}

Answer 12

This is simple and works pretty well:

function twoDigit(number) {
  var twodigit = number >= 10 ? number : "0"+number.toString();
  return twodigit;
}

Answer 13

Here's the easiest solution I found:-

let num = 9; // any number between 0 & 99
let result = ( '0' + num ).substr( -2 );

Answer 14

Improved version of previous answer

function atLeast2Digit(n){
    n = parseInt(n); //ex. if already passed '05' it will be converted to number 5
    var ret = n > 9 ? "" + n: "0" + n;
    return ret;
}

alert(atLeast2Digit(5));

Answer 15

I know this is an ancient post, but I wanted to provide a more flexible and OO solution option.

I've extrapolated the accepted answer a bit and extended javascript's Number object to allow for adjustable zero padding:

Number.prototype.zeroPad = function(digits) {
  var loop = digits;
  var zeros = "";
  while (loop) {
    zeros += "0";
    loop--;
  }
  return (this.toString().length > digits) ?
    this.toString() : (zeros + this).slice(-digits);
}
var v = 5;
console.log(v.zeroPad(2)); // returns "05"
console.log(v.zeroPad(4)); // returns "0005"

Edit: Add code to prevent cutting off numbers longer than your requested digits.

NOTE: This is obsolete in all but IE. Use padStart() instead.

Answer 16

There is not a built-in number formatter for JavaScript, but there are some libraries that accomplish this:

1. underscore.string provides an sprintf function (along with many other useful formatters)
2. javascript-sprintf, which underscore.string borrows from.

Answer 17

My version:

`${Math.trunc(num / 10)}${Math.trunc(num % 10)}`;

const func = (num) => `${Math.trunc(num / 10)}${Math.trunc(num % 10)}`;

const nums = [1, 3, 5, 6, 8, 9, 10, 20, 56, 80];
nums.forEach(num => console.log(func(num)));

Answer 18

You can use the padStart method:

more info: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart

function n(num, len = 2) {
  return `${num}`.padStart(len, '0');
}

console.log(n( 9));   //print "09"
console.log(n(10));   //print "10"
console.log(n(999));  //print "999"
console.log(n(999,6));//print "000999"

Answer 19

or

function zpad(n,l){
   return rep(l-n.toString().length, '0') + n.toString();
}

with

function rep(len, chr) { 
   return new Array(len+1).join(chr);
}

Answer 20

If you want to limit your digits at the same time:

function pad2(number) {
  number = (number < 10 ? '0' : '') + number;
  number = number.substring(0,2);
  return number;
}

This would also chop of any value that exceeds two digits. I have been extending this upon fanaur's solution.

Answer 21

`${number}`.replace(/^(\d)$/, '0$1');

Regex is the best.

Answer 22

Updated for ES6 Arrow Functions (Supported in almost all modern browsers, see CanIUse)

const formatNumber = n => ("0" + n).slice(-2);

Answer 23

<html>
    <head>
        <script src="http://code.jquery.com/jquery-1.11.0.min.js"></script>
        <script type="text/javascript">
            $(document).ready(function(){
                $('#test').keypress(allowOnlyTwoPositiveDigts);
            });

            function allowOnlyTwoPositiveDigts(e){

                var test = /^[\-]?[0-9]{1,2}?$/
                return test.test(this.value+String.fromCharCode(e.which))
            }

        </script>
    </head>
    <body>
        <input id="test" type="text" />
    </body>
</html>

Answer 24

Here's a simple recursive solution that works for any number of digits.

function numToNDigitStr(num, n)
{
    if(num >=  Math.pow(10, n - 1)) { return num; }
    return "0" + numToNDigitStr(num, n-1);
}

Answer 25

If you don't have lodash in your project it will be an overkill to add the whole library just to use one function. This is the most sophisticated solution of your problem I've ever seen.

_.padStart(num, 2, '0')

Answer 26

I built a pretty simple format function that I call whenever I need a simple date formatted. It deals with formatting single digits to double digits when they're less than 10. It kicks out a date formatted as Sat Sep 29 2018 - 00:05:44

This function is used as part of a utils variable so it's called as:

let timestamp = utils._dateFormatter('your date string');

var utils = {
  _dateFormatter: function(dateString) {
    let d = new Date(dateString);
    let hours = d.getHours();
    let minutes = d.getMinutes();
    let seconds = d.getSeconds();
    d = d.toDateString();
    if (hours < 10) {
      hours = '0' + hours;
    }
    if (minutes < 10) {
      minutes = '0' + minutes;
    }
    if (seconds < 10) {
      seconds = '0' + seconds;
    }
    let formattedDate = d + ' - ' + hours + ':' + minutes + ':' + seconds;
    return formattedDate;
  }
}

Answer 27

My Example like this

         var n =9;
         var checkval=('00'+n).slice(-2);
         console.log(checkval)

and the output is 09

Answer 28

Here's my version. Can easily be adapted to other scenarios.

function setNumericFormat(value) {
    var length = value.toString().length;
    if (length < 4) {
        var prefix = "";
        for (var i = 1; i <= 4 - length; i++) {
            prefix += "0";
        }
        return prefix + value.toString();
    }
    return  value.toString();
}

Answer 29

    function colorOf(r,g,b){
  var f = function (x) {
    return (x<16 ? '0' : '') + x.toString(16) 
  };

  return "#" +  f(r) + f(g) + f(b);
}

Answer 30

For anyone who wants to have time differences and have results that can take negative numbers here is a good one. pad(3) = "03", pad(-2) = "-02", pad(-234) = "-234"

pad = function(n){
  if(n >= 0){
    return n > 9 ? "" + n : "0" + n;
  }else{
    return n < -9 ? "" + n : "-0" + Math.abs(n);
  }
}