Let's imagine that you created a giveaway application, and today is the raffle. Unfortunately, you have a list of 10 participants, but you don't know how to select randomly one of them as a winner.
Don't worry! In a few minutes, you will be able to get a random element from an array in JavaScript!
How to Select a Random Element from an Array using the Mathematical functions
Here is the one line instruction to get a a random element from your array: YOUR_ARRAY[Math.floor(Math.random() * YOUR_ARRAY.length)]
.
Let's break this instruction and understand what it does:

YOUR_ARRAY
is your array variable (in that case, the 10 participants email addresses) 
YOUR_ARRAY.length
is an array property that returns the size of your array 
Math.random()
is a function that returns a pseudorandom number in the range 0 to less than 1 (inclusive of 0, but not 1) 
Math.floor()
is a function that returns the largest integer less than or equal to a given number
Note: As Mozilla mentions,
Math.random()
does not provide cryptographically secure random numbers. It's not recommended to use them for anything related to security. Use the Web Crypto API instead, and more precisely, the window.crypto.getRandomValues() method.
Now you know each instruction, let me show you a stepbystep example:
const participants = [
'test1@herewecode.io',
'test2@herewecode.io',
'test3@herewecode.io',
'test4@herewecode.io',
'test5@herewecode.io',
'test6@herewecode.io',
'test7@herewecode.io',
'test8@herewecode.io',
'test9@herewecode.io',
'test10@herewecode.io',
]
console.log(participants.length)
// Output: 10
console.log(Math.random())
// Output: random number between 0 or 1 (ex: 0.623242121481016)
console.log(Math.random() * participants.length)
// Output: random number between 0 or 1 multiplied by 10 (ex: 0.623242121481016 * 10 = 1.6905986987355703)
console.log(Math.floor(Math.random() * participants.length))
// Output: it takes the larger integer less than or equal to a given number (ex: Math.floor(1.6905986987355703) = 1)
Note: If you try the code above, the result will always be different because of the
Math.random()
function.
Here we are! It's time to select the giveaway winner! To do so, we will use what we learned in this article and use it with your use case:
const participants = [
'test1@herewecode.io',
'test2@herewecode.io',
'test3@herewecode.io',
'test4@herewecode.io',
'test5@herewecode.io',
'test6@herewecode.io',
'test7@herewecode.io',
'test8@herewecode.io',
'test9@herewecode.io',
'test10@herewecode.io',
] // 10 participants
const winner = participants[Math.floor(Math.random() * participants.length)]
console.log(winner)
// Output is random (launch this code to see who is the winner :D)
So! Who won the jackpot? 😉
➡️ I help web developers improve their skills 💻 If you want to get more tips and resources about web programming > Follow me on Twitter 🐦
Top comments (4)
You may want to be a bit clearer in your description of
Math.random()
 it can never return1
, but it can return0
That's right, thanks for the feedback! I'm updating the article right now! 😉
You are right, maybe with  0 can write shorter:
Oh, I like the idea! I just tried it, and it seems to work well! Thanks for sharing that! 🙏
I also like the idea of creating a generic function to get a pseudorandom value from a list.