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Oyetoke Toby
Oyetoke Toby

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Javascript Random String Fastest Way to Generate Random Strings in JavaScript

There are so many ways to generate random strings in JavaScript and it doesn't really matter which method is faster.

The method I like using most is Math.random()

I made a video on it:

Basically the idea is to use Math.random(), then you can convert it to string and do some simple string manipulation on it.

To get random numbers, I would use something like below:


To get random strings with numbers only, I would use:

Math.random().toString().substr(2, 5)

Fortunate .toString() has a param called radix that you can pass in numbers between 2 - 36 which will cast the generated numbers to the radix characters that fall between the given number. The radix is also known as base and its for representing numeric values

To get a random number between 0-1:

Math.random().toString(2).substr(2, 5)

To get a random number between 0-5:

Math.random().toString(5).substr(2, 5)

Starting from 11/12, it will start introducing letters. So to get a fully random string:

Math.random().toString(20).substr(2, 6)

With this you can now write your awesome random string generator:

const generateRandomString = function(){
return Math.random().toString(20).substr(2, 6)

To be able to change the length of the output:

const generateRandomString = function(length=6){
return Math.random().toString(20).substr(2, length)

One liner

const generateRandomString = (length=6)=>Math.random().toString(20).substr(2, length)

That's all.

If you know of any other faster ways, please I would love to see it in the comment section.


Top comments (7)

wwaterman12 profile image

Nice function! But one thing I noticed is that this will only work for random alpha-numeric strings up to a certain length. If you want to have something longer, you should call the method recursively. Something like:

const generateRandomString = function (length, randomString="") {
  randomString += Math.random().toString(20).substr(2, length);
  if (randomString.length > length) return randomString.slice(0, length);
  return generateRandomString(length, randomString);
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rohaq profile image
Richard Hodgson

Yep, looks like it tops out at 12-13 characters for me, demo here:

pcbailey profile image
Phillip Rhodes

Hi, thanks for the simple, straight-forward article! I just wanted to point out a small error in your one-liner. You define the length variable, but you still used a hard-coded "6" instead of it in the expression.

maulerjan profile image
Jan Mauler

Don't use the .substr(2, ...) at the end, because you risk having empty string as a result. The result of Math.random() can be 0, so if you substr(2, ...), you will end up with an empty string.

diek profile image

Do you like base20 for something special?

oyetoket profile image
Oyetoke Toby

No reason actually, I just like using it.

austindd profile image

Just to clarify for people who don't know, the radix argument for toString goes from 2 to 36, and you need to use 36 to include all alphanumeric characters in the alphabet. Using 20 will omit more than half of the alphabetic letters from the output.