JavaScript Pad a number with leading zeros

The String prototype property is used to pad a number with leading zeros. This property allows for adding new properties and methods to existing object types. 

Syntax:

object.prototype.name = value

Return value: It returns a reference to the String.prototype object. 

Example 1: This example adds leading zeros to a number by creating a function and inside this function, if the number is less than the width provided then it adds the leading zeros. 

html

<h1 style="color:green;">
    GeeksforGeeks
</h1>

<p id="GFG_UP" style="font-size: 16px;"></p>

<button onclick="gfg_Run()">
    click here
</button>

<p id="GFG_DOWN" style="color:green;
                    font-size: 20px; font-weight: bold;">
</p>

<script>
    var el_up = document.getElementById("GFG_UP");
    var el_down = document.getElementById("GFG_DOWN");
    var num = 2213;
    el_up.innerHTML = 'Number = ' +num;
    function pad(n, width) {
        n = n + '';
        return n.length >= width ? n :
            new Array(width - n.length + 1).join('0') + n;
    }
    function gfg_Run() {
        el_down.innerHTML = pad(num, 7);
    }
</script>

Output:

JavaScript Pad a number with leading zeros

Example 2: This example adds leading zeros to a number by creating a prototype pad. In this example we can pass a string to the object, whatever we want to pad with the number. 

html

<h1 style="color:green;">
    GeeksForGeeks
</h1>

<p id="GFG_UP" style="font-size: 16px;"></p>

<button onclick="gfg_Run()">
    click here
</button>

<p id="GFG_DOWN" style="color:green;
                font-size: 20px; font-weight: bold;">
</p>

<script>
    var el_up = document.getElementById("GFG_UP");
    var el_down = document.getElementById("GFG_DOWN");
    var num = '2213';
    el_up.innerHTML = 'Number = ' + num;

    String.prototype.pad = function(String, len) {
        var str = this;
        while (str.length < len)
            str = String + str;
        return str;
    }
    function gfg_Run() {
        el_down.innerHTML = num.pad("0", 9);
    }
</script>

Output:

JavaScript Pad a number with leading zeros