Javascript adding zeros to the beginning of a string (max length 4 chars)

Question

var number = 1310;

should be left alone.

var number = 120;

should be changed to \"0120\";

var num         


        

Answer 1

Use String.JS librairy function padLeft:

S('123').padLeft(5, '0').s   --> 00123

Answer 2

try these:

('0000' + number).slice(-4);

or

(number+'').padStart(4,'0');

Answer 3

//to: 0 - to left, 1 - to right
String.prototype.pad = function(_char, len, to) {
    if (!this || !_char || this.length >= len) {
        return this;
    }
    to = to || 0;

    var ret = this;

    var max = (len - this.length)/_char.length + 1;
    while (--max) {
        ret = (to) ? ret + _char : _char + ret;
    }

    return ret;
};

Usage:

someString.pad(neededChars, neededLength)

Example:

'332'.pad('0', 6); //'000332'
'332'.pad('0', 6, 1); //'332000'

Answer 4

Nate as the best way I found, it's just way too long to read. So I provide you with 3 simples solutions.

1. So here's my simplification of Nate's answer.

//number = 42
"0000".substring(number.toString().length, 4) + number;

2. Here's a solution that make it more reusable by using a function that takes the number and the desired length in parameters.

function pad_with_zeroes(number, len) {
  var zeroes = "0".repeat(len);
  return zeroes.substring(number.toString().length, len) + number;
}

// Usage: pad_with_zeroes(42,4);
// Returns "0042"

3. Here's a third solution, extending the Number prototype.

Number.prototype.toStringMinLen = function(len) {
  var zeroes = "0".repeat(len);
  return zeroes.substring(self.toString().length, len) + self;
}

//Usage: tmp=42; tmp.toStringMinLen(4)

Answer 5

In all modern browsers you can use

numberStr.padStart(4, "0");

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

function zeroPad(num) {
  return num.toString().padStart(4, "0");
}

var numbers = [1310, 120, 10, 7];

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

    console.log(paddedNum);
  }
);