Oyetoke Toby

Posted on Feb 10, 2020 • Updated on Jun 2, 2020

Javascript Random String Fastest Way to Generate Random Strings in JavaScript

#javascript #showdev

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:

Math.ceil(Math.random()*10000)

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.

Thanks

Top comments (7)

wwaterman12 • Jul 8 '20

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);
};

rohaq • Feb 14 '21

Yep, looks like it tops out at 12-13 characters for me, demo here: jsfiddle.net/mberwk8a/2/

Phillip Rhodes • May 29 '20

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.

diek • Feb 12 '20

Do you like base20 for something special?

Oyetoke Toby • Feb 13 '20

No reason actually, I just like using it.

Austin • Feb 19 '21

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.

Jan Mauler • Nov 6 '22

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.

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Javascript Random String Fastest Way to Generate Random Strings in JavaScript

Top comments (7)

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