Generate random alpha-numeric string in JavaScript

The task is to generate a random alpha-numeric string of specified length using javascript, we’re going to discuss few techniques. 

Approach 1:

• Creates a function which takes 2 arguments one is the length of the string that we want to generate and another is the characters that we want to be present in the string.
• Declare new variable ans = ‘ ‘.
• Traverse the string in reverse order using for loop.
• Use JavaScript Math.random() method to generate the random index and multiple with the length of string.
• Use JavaScript Math.floor( ) to round off it and add into the ans.

Example 1: This example uses the Math.random() method to generate the random index and then appends the character from the string we passed. 

html

<h1 style="color:green;">
    GeeksforGeeks
</h1>
<p id="GFG_UP">
</p>
<button onClick="GFG_Fun()">
    click here
</button>
<p id="GFG_DOWN">
</p>
<script>
    var up = document.getElementById('GFG_UP');
    var down = document.getElementById('GFG_DOWN');
    up.innerHTML =
    'Click on the button to generate alpha-numeric string';

    function randomStr(len, arr) {
        var ans = '';
        for (var i = len; i > 0; i--) {
            ans +=
            arr[Math.floor(Math.random() * arr.length)];
        }
        return ans;
    }

    function GFG_Fun() {
        down.innerHTML = randomStr(20, '12345abcde');
    }
</script>

Output:

Generate random alpha-numeric string in JavaScript

Approach 2:

• First generate a random number using Math.random() method.
• Use JavaScript toString(36) to convert it into base 36 (26 char + 0 to 9) which is also alpha-numeric string.
• Use JavaScript String.slice() method to get the part of string which is started from position 2.

Example 2: This example first generate a random number(0-1) and then converts it to base 36 which is also alpha-numeric string by using toString(36)() method. 

html

<h1 style="color:green;">
    GeeksforGeeks
</h1>
<p id="GFG_UP">
</p>
<button onClick="GFG_Fun()">
    click here
</button>
<p id="GFG_DOWN"> </p>
<script>
    var up = document.getElementById('GFG_UP');
    var down = document.getElementById('GFG_DOWN');
    up.innerHTML =
    'Click on the button to generate alpha-numeric string';

    function GFG_Fun() {
        down.innerHTML =
        Math.random().toString(36).slice(2);
    }
</script>

Output:

Generate random alpha-numeric string in JavaScript