HOW TO GENERATE 4 DIGIT OTP WITH JAVASCRIPT

Are you looking to generate OTP codes for your application for authentication?
Follow these few steps and you will be able to do that.

STEP 1
Generate a random number between 0 and 9000

const randomNum = Math.random() * 9000
console.log(randomNum)

// will log random numbers like (1758.36816277815,8591.126356595876,380.85504639047053)

STEP 2
Format the random number, to eliminate the decimals

const randomNum = Math.random() * 9000
const formattedRandomNum = Math.floor(randomNum)
console.log(formattedRandomNum)

// will log random numbers like (1758,8591,380)

STEP 3
Add 1000 to the generated value to make sure the length is always 4.

Note: Math.random() will generate random numbers between 0 and 8999, so adding 1000 to this random number, the highest can only be 9999, so our max length of 4 is always ensured and preserved.

const randomNum = Math.random() * 9000
const token = Math.floor(1000 + randomNum)
console.log(token)

// will log random numbers like (2758,9591,1380)

STEP 4
Refactor into a function you can call each time you need to generate a token.

function generateToken(){
   const randomNum = Math.random() * 9000
   return Math.floor(1000 + randomNum)
}

// will log random numbers like (2758,9591,1380)

STEP 5
Call the function and your token is generated, then you can go ahead and hash the code/use it for what you intent.

function generateToken(){
   const randomNum = Math.random() * 9000
   return Math.floor(1000 + randomNum)
}

generateToken() 
// will return random numbers like (2758,9591,1380)

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Comments

[Jon Randy 🎖️]

Why not just pad with zeros to preserve length? Then there are more potential codes...

const generateToken = ()=>`${~~(Math.random()*10e3)}`.padStart(4,0)

[Candie]

That works too.

[RRNauhwar]

not correct, Token will be generate in string form.
const otpGenerator = () => Math.floor(Math.random()*9000)+1000
console.log(otpGenerator())

[Jon Randy 🎖️]

This will have all codes from 0000 to 0999 missing.

We're generating a 4 digit OTP to be used effectively as a temporary password. Digits are from 0-9. If we choose to generate a string, it doesn't matter since we'll be using it in a string-like context anyway. Using a string allows for 1000 more possible codes than just using an integer.