JavaScript Program for Generating a String of Specific Length
Last Updated :
23 Jul, 2025
In this article, we are going to discuss how can we generate a string having a specific length. You might encounter many situations when working with JavaScript where you need to produce a string with a specified length. This could be done for a number of reasons, including generating passwords, unique IDs, or formatting data for display.
Using For Loop
- In this approach, we initialize an empty string result and use a loop to generate random characters and concatenate them to the result until the desired length is achieved.
- Create a characters array containing all the characters that you allow to be in your string.
- Create a variable "str" to store your string & iterate "n" times.
- Inside the for loop generate a random index using Math.random() and store it in a variable.
- Select the character present at the previously generated random index from your character array and append it to the previously created "str".
- After the loop ends you will have your "n" length string in the variable "str".
Example: This example shows the use of the above-explained approach.
JavaScript
function getString(n) {
let str = '';
const characters =
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
const charLen = characters.length;
for (let i = 0; i < n; i++) {
// Generating a random index
const idx = Math.floor(Math.random() * charLen);
str += characters.charAt(idx);
}
return str;
}
const result = getString(10);
console.log(result);
- Here, we select a random character from the given character set and use the repeat() method to repeat it the desired number of times.
- Create a characters array containing all the characters that you allow to be in your string.
- Generate a random index using Math.random() and store it in a variable.
- Select the character present at previously generated random index from your character array. And use repeat() method to repeat the character "n" times.
Example: This example shows the use of the above-explained approach.
JavaScript
function getString(n) {
const characters =
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
const charLen = characters.length;
// Generating a random index
const idx = Math.floor(Math.random() * charLen);
// Using above generated random index
// and extracting the corresponding
// character from "characters" array
const ch = characters.charAt(idx);
// Using repeat method to repeat
// the character "n" times.
return ch.repeat(n);
}
const result = getString(10);
console.log(result);
Using Array Manipulation
- In this approach, we push random characters into an array and then use the join() method to convert the array into a string.
- Create a characters array containing all the characters that you allow to be in your string.
- Create an empty array "resultArray" to store characters. And iterate it "n" times.
- Inside the for loop generate a random index using Math.random() and store it in a variable.
- Select the character present at previously generated random index from your character array and push it in the previously created "resultArray".
- After the loop ends you will have your "n" characters stored in your array "resultArray". Use join() method to join all the characters in the array as a string.
Example: This example shows the use of the above-explained approach.
JavaScript
function getString(n) {
const characters =
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
const charLen = characters.length;
const resultArray = [];
for (let i = 0; i < n; i++) {
// Generating a random index
const idx = Math.floor(Math.random() * charLen);
// Pushing the corresponding
// character to the array
resultArray.push(characters.charAt(idx));
}
// Joining all the characters of the array
return resultArray.join('');
}
const result = getString(10);
console.log(result);
Using Array.from()
To generate a string of a specific length using `Array.from()`, create an array with the desired length using `{ length }`. Fill it with the specified character using the mapping function, then join the array into a string.
Example:
JavaScript
function generateString(length, char) {
return Array.from({ length }, () => char).join('');
}
// Example usage:
const length = 5;
const character = '*';
console.log(generateString(length, character));
Using Crypto Module
The crypto module in Node.js provides cryptographic functionality that can help in generating secure random strings. By leveraging crypto.randomBytes, we can generate a buffer of random bytes and convert it into a string.
Example: This example demonstrates the use of the crypto module to generate a random string of the desired length.
JavaScript
const crypto = require('crypto');
function getSecureString(length) {
const characters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
const charLen = characters.length;
// Generate random bytes
const randomBytes = crypto.randomBytes(length);
let result = '';
for (let i = 0; i < length; i++) {
// Use each byte value to select a character from the allowed set
const idx = randomBytes[i] % charLen;
result += characters.charAt(idx);
}
return result;
}
const result = getSecureString(10);
console.log(result);
Similar Reads
JavaScript Program to Truncate a String to a Certain Length In this article, we are going to learn how can we truncate a string to a certain length. Truncating a string to a certain length in JavaScript means shortening a string so that it doesn't exceed a specified maximum length. This can be useful for displaying text in user interfaces, such as titles or
3 min read
JavaScript Program to Generate a Range of Numbers and Characters Generating a range of numbers and characters means creating a sequential series of numerical values or characters, typically within specified start and end points, forming a continuous sequence or collection. Approaches to Generate a Range of Numbers and Characters Using JavaScriptTable of Content U
4 min read
JavaScript Program to Print all Subsequences of a String A subsequence is a sequence that can be derived from another sequence by deleting zero or more elements without changing the order of the remaining elements. Subsequences of a string can be found with different methods here, we are using the Recursion method, Iteration method and Bit manipulation me
3 min read
JavaScript - How to Pad a String to Get the Determined Length? Here are different ways to pad a stirng to get the specified length in JavaScript.1. Using padStart() MethodThe padStart() method can be used to pad a string with the specified characters to the specified length. It takes two parameters, the target length, and the string to be replaced with. If a nu
3 min read
Java Program to Convert Long to String The long to String conversion in Java generally comes in need when we have to display a long number in a GUI application because everything is displayed in string form. In this article, we will learn about Java Programs to convert long to String. Given a Long number, the task is to convert it into a
4 min read
Java Program to Count Number of Digits in a String The string is a sequence of characters. In java, objects of String are immutable. Immutable means that once an object is created, it's content can't change. Complete traversal in the string is required to find the total number of digits in a string. Examples: Input : string = "GeeksforGeeks password
2 min read