setTimeout not working

JavaScript
1

I am trying to make a slider, and I don’t think setTimeout is working…

<script>

for (c=1;c>0;c++) {
	var a = document.getElementsByClassName('sliderimage').length;

		for (b=0;b<=a;b++) {
			
			var g = document.getElementsByClassName('sliderimage');
			g[b].style.display = 'block';		
			
			var h = setTimeout(f,5000);
			function f() {g[b].style.display = 'none';};
		};
	};
	
</script>
2

missing let or var.

missing let or var.

This will set all elements to style block, and then 5 seconds later turn off the last one.

I suspect what you’re actually wanting to do is something more like…

let cur = 0; //Note: I assume the first sliderimage is already set to display 'block'.
let sliders = document.getElementsByClassName('sliderimage');
setInterval(function() {
  sliders[cur].style.display = "none";
  cur = ++cur % sliders.length;
  sliders[cur].style.display = "block";
}, 5000);
2 Likes
3

why does this set all elements to block, and not just one using the array of variable “b” ? I thought it would loop through one at a time.

4

It will - but it doesnt STOP.

setTimeout doesnt tell the script “wait here for 5 seconds, then proceed”, it tells the script “in 5 seconds do this, meanwhile continue doing whatever you’re doing.” (This, for technical reference, is called an asynchronous operation. The main thread of the engine keeps parsing, while a secondary thread holds onto the request and processes it accordingly.)

So it will run through all the loops of b at the same time. (well, one after another, but without pausing)

1 Like
5

to give a (sadly) more real world example, if you’ve got any sort of smart assistant in your home, you can tell it “[AssistantName] start a timer for 5 minutes”.

Your script is saying that b times over; the assistant will happily keep setting timers for you, and 5 minutes from now, a royal cocophany goes off as b different timers all start going off at the same time (plus or minus the amount of time it took you to say “start a timer for 5 minutes”).

6

ok, i get it. Thanks