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JavaScript Callback Functions in JavaScript Callbacks with Timers Using Anonymous Functions with setInterval

Posted by Nick Burton
Nick Burton
7,387 Points

How to run setInterval() with dynamic delay value

I understand how I would generate a random number and pass it into the setInterval function to consistently "tick" with the generated delay in between each tick. But, what if I wanted to have a dynamic delay for each tick? Meaning the time gap between each tick would be different every time. I tried to pass a function to generate the delay but it seems to only be executed once. Here's my code that doesn't work:

const randNumGenerator = () => (Math.floor(Math.random() * 5) + 1) * 1000;

setInterval(() => {
  console.log('tick');
}, randNumGenerator());

Can someone explain to me how to go about this or point me in the right direction? Thanks!

2 Answers

Steven Parker
Steven Parker
229,744 Points
Steven Parker
Steven Parker
229,744 Points

The random generator is only called once, and then the "setInterval" function just repeats that setting over and over. But you can set fresh conditions for each tick by using a wrapper function to set a single timeout and then have it call itself when the tick occurs to set up the next one:

function randomTick() {
  setTimeout(() => {
    console.log("tick");
    randomTick();  // set up the next tick
  }, randNumGenerator());
}
randomTick();      // start the first tick
Nick Burton
Nick Burton
7,387 Points

Woah, that's clever! Thank you for taking the time to respond with that example.

<noob />
<noob />
17,062 Points
<noob />
<noob />
17,062 Points

Steven Parker i would like to know if there is a way to, the closet thing i got is to set it evreytime the page load to have a diff delay

function tickClock() {
  clockSection.textContent = getTime();

}


tickClock();
setInterval(tickClock,Math.random() * 4000);