# How to generate a random string in JavaScript

By Atta Ur Rehman Shah (https://attacomsian.com/about). Published Oct 23, 2020. Topics: JavaScript.
Canonical URL: https://attacomsian.com/blog/javascript-generate-random-string

> A quick guide to learn how to generate random strings of different sizes in JavaScript.

There are many ways available to generate a random string in JavaScript. The quickest way is to use the `Math.random()` method.

The `Math.random()` method returns a random number between 0 (inclusive),  and 1 (exclusive). You can convert this random number to a string and then remove the trailing zeros:

```javascript
const rand = Math.random().toString().substr(2, 8);  // 60502138
```

The above code will generate a random string of 8 characters that will contain numbers only.  

To generate an alpha-numeric string, you can pass an integer value between `2` and `36` to the `toString()` method called `radix`. It defines the base to use for representing a numeric value.

For a binary string (0-1), you can pass `2` as `radix` to `toString()`:

```javascript
const binary = Math.random().toString(2).substr(2, 8);  // 01100110
```

To generate a fully random string, you should pass `16` or greater as a `radix` value to `toString()`:

```javascript
const rand = Math.random().toString(16).substr(2, 8); // 6de5ccda
```

Let us write a function by using the above code to generate a random string anywhere between 0 and 14 characters:

```javascript
const random = (length = 8) => {
    return Math.random().toString(16).substr(2, length);
};

console.log(random()); // bb325d9f
console.log(random(6)); // e51d83
console.log(random(10)); // e84c416cc7
console.log(random(14)); // ee16dfc68e361
```

## Generate large random strings

To generate large random strings (14+ characters long), you have to write your own generator. The following example demonstrates how you can generate strings of any size by picking characters randomly from `A-Z`, `a-z`, and `0-9`:

```javascript
const random = (length = 8) => {
    // Declare all characters
    let chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';

    // Pick characers randomly
    let str = '';
    for (let i = 0; i < length; i++) {
        str += chars.charAt(Math.floor(Math.random() * chars.length));
    }

    return str;

};

console.log(random()); // JgKGQEUx
console.log(random(12)); // ttwbeshkYzaX
console.log(random(20)); // zZN7uH9pPjhJf30QNus5
```

In the above example, `Math.random()` and `Math.floor()` methods are used to generate a random index of the character in the specified characters (A-Z a-z 0-9).

The [for loop](https://attacomsian.com/blog/javascript-loops) is used to loop through the number passed into the `random()` function. During each iteration of the loop, a random character is selected from the characters' list.