Skip to content

How do I prevent a duplicate random number when using setInterval? (javascript)

I’ve been wanting to generate random numbers through a function and then use setInterval to repeat that function and give me a new number every time.

function randNum(prevNum) { 
    let randNum = Math.round(Math.random() * 12)     //choose a number between 0 and 12 
    while (randNum == prevNum){                //if the chosen number is the same as prevNum, choose another random number
        randColor = Math.round(Math.random() * 12) 
    prevNum = randColor            //assign current value to parameter 
    return (prevNum);              //return parameter

prevNum = 0,
prevNum = setInterval (randNum, 1000, prevNum)     //assign returned parameter to current variable, then go back into the function with the new parameter value.

also using node so semicolons might be missing.


When you use prevNum as a setInterval() argument, you’re always passing the original value of the variable to the callback function. You should just use the global variable directly rather than passing it as a parameter.

You also have a typo, randColor should be randNum.

let prevNum = 0;

function randNum() {
  let newNum
  while (true) {
    newNum = Math.round(Math.random() * 12) //choose a number between 0 and 12 
    if (newNum != prevNum) {
  prevNum = newNum //save the current value

let interval = setInterval(randNum, 1000)

The return value of the callback function isn’t used, so there’s no point in return prevNum;. And you shouldn’t assign the result of setInterval() to your number variable — it returns a timer ID, not the value of the function.