How to Generate a Random String in JavaScript

For one reason or another, you might be wondering how to generate a random string in JavaScript.

Thankfully, there are many different ways to approach this problem.

In this post, we will be looking at how to generate a random string with binary characters, hexadecimal characters, and then one where you can specify the characters you want to use.

Generating a random string with binary characters

In all of the examples, we will take advantage of the Math.random() function. This function returns a random number between 0 and 1.

From there, we can convert it to a string:

JAVASCRIPT
const randomNumber = Math.random().toString(2);

console.log(randomNumber);

BASH
0.1101011011110101010110110001101111110110100100110001

Now we can use the substr() method to skip the first two characters and cut off the number at a length of 8:

JAVASCRIPT
const randomNumber = Math.random().toString(2);

const randomString = randomNumber.substr(2, 8);

console.log(randomString);

BASH
00001101

Here is a re-usable function:

JAVASCRIPT
const generateRandomBinary = (length) => {
    const randomNumber = Math.random().toString(2);

    return randomNumber.substr(2, length);
};

BASH
0110

Generating a random string with hexadecimal characters

For this, we will reuse the previous code, except change the radix of the toString() method.

This will return a hexadecimal number instead of a binary one:

JAVASCRIPT
const randomNumber = Math.random().toString(16);

const randomString = randomNumber.substr(2, 8);

console.log(randomString);

BASH
69ee0964

Here is a re-usable function:

JAVASCRIPT
const generateRandomHex = (length) => {
    const randomNumber = Math.random().toString(16);

    return randomNumber.substr(2, length);
};

BASH
c142

Generating a random string with a custom character set

For this, we will need to use a different implementation.

First, let's define the set of characters we want to use:

JAVASCRIPT
const characters = "abcdefghijklmnopqrstuvwxyz0123456789";

Now let's select from the set a random character:

JAVASCRIPT
const randomCharacter = characters[Math.floor(Math.random() * characters.length)];

Now, let's make a method that takes in a length and returns a random string of that length:

JAVASCRIPT
const characters = "abcdefghijklmnopqrstuvwxyz0123456789";

const generateRandomString = (length) => {
    let randomString = "";

    for (let i = 0; i < length; i++) {
        randomString += characters[Math.floor(Math.random() * characters.length)];
    }

    return randomString;
};

console.log(generateRandomString(8));

BASH
6vudynt3

Conclusion

In this post, we took a look at how to randomly generate binary, hexadecimal, and custom strings.

From here, you can use for anything ranging from hashing to generating seeds.

Thanks for reading!

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