JavaScript - generate random string of size n characters

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In this article, we would like to show you how to generate a random string in JavaScript.

In the below example, randrom string is generated using predefined alphabet. The string is generated by seleting random characters from the alphabet.

Runnable example:

// ONLINE-RUNNER:browser;

var alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';

function randomString(length) {
    var result  = '';
    for (var i = 0; i < length; ++i) {
        result += alphabet[Math.floor(alphabet.length * Math.random())];
    return result;

// Usage example:
//                             // Example random strings:
console.log(randomString(5));  // VhMsQ
console.log(randomString(10)); // eVOznvSxWw
console.log(randomString(20)); // ZZomN9sxyaL9vfsGE3to



  1. Math.random() - MDN Web Docs 
  2. Math.floor() - MDN Web Docs
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JavaScript - String (popular problems)

JavaScript - generate random string of size n characters
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