javascript - Using Random Number Generator for a Loop Timeout

Question

This script should scroll through each container on a website with a randomly generated delay. I want to replace the "pause" of 2000ms with a randomly generated number between min and max seconds for each iteration in the loop.

var min = 3,
    max = 9;
var y = document.querySelectorAll('.chunk-container').length;

for (let x=0; x<y; x++) {
   task(x);
}

function task(x) {
//    var z = randomGen() * 1000;
    setTimeout(function() {
        console.log('X = ' + x + ' Y = ' + y);
            document.getElementsByClassName('chunk chunk-container')[x].scrollIntoView({behavior: 'smooth'});
            console.log('Scrolled to next Container');
    }, /* z */ 2000 * x);
}
})

Random number generator:

function randomGen() {
    var rand = Math.floor(Math.random() * (max - min + 1) + min);
    console.log('Random Number generated: ' + rand + ' seconds');
    return rand;
}

Like this it works fine. After each iteration, there is a 2 second pause. However when I remove the comments to add the lines var z = randomGen() * 1000; to randomize the time between each iteration, the x value (at which container it should scroll to) starts off fine, but then turns out random as well.

The console output:

Random Number generated: 6 seconds
Random Number generated: 5 seconds
Random Number generated: 4 seconds
Random Number generated: 8 seconds
Random Number generated: 4 seconds
Random Number generated: 8 seconds
X = 0 Y = 7
Scrolled to next Container
X = 1 Y = 7
Scrolled to next Container
X = 2 Y = 7
Scrolled to next Container
X = 4 Y = 7
Scrolled to next Container
X = 3 Y = 7
Scrolled to next Container
X = 5 Y = 7
Scrolled to next Container
X = 6 Y = 7
Scrolled to next Container

How can I fix this?

question from:https://stackoverflow.com/questions/65908073/using-random-number-generator-for-a-loop-timeout

Answer 1

I rewrote you code. I think the main problem was that setTimeout is non blocking. I used promise together with await to solve it

function sleep(time) {
    return new Promise(resolve => setTimeout(resolve, time));
}

function randomGen(max, min) {
    return Math.floor(Math.random() * (max - min + 1) + min);
}

async function randomWaitAndScroll(elements, timeMin, timeMax) {
  for (element of elements) {
    let random = randomGen(timeMin, timeMax)
    await sleep(random);
    element.scrollIntoView({behavior: 'smooth'});
  }
}

const containerElements = document.querySelectorAll('.chunk-container');
randomWaitAndScroll(containerElements, 3000, 9000);