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Generate random alpha-numeric string in JavaScript

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In this article with the help of javascript  we are generating the alpha-numeric string of specific length using javascript, here are some common method 

Approach 1:

  • Creates a function that 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 the string.
  • Use JavaScript Math.floor( ) to round off it and add it 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. 


function randomStr(len, arr) {
    let ans = '';
    for (let i = len; i > 0; i--) {
        ans +=
            arr[(Math.floor(Math.random() * arr.length))];
randomStr(20, '12345abcde');



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 an alpha-numeric string.
  • Use JavaScript String.slice() method to get the part of the string which is started from position 2.

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


function GFG_Fun() {


Last Updated : 05 Jun, 2023
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