How to use setInterval or setTimeout with a for loop?

I am trying to set an interval when some code runs but only need to do it based on the number of elements there are. Here's a quick example:

5 total elements

Run code once every 20 seconds for each element that is found.

Can someone please give me a basic example how to do this using plain JavaScript? Everything I have tried just executes all of the code at once instead of doing one element at a time.



let's suppose you're talking about elements of an array or a DOM collection

(function() {
   var arr = [...],
       len = arr.length;

   (function doProcess() {
       if (len--) {
           /* do something with arr[len] */
           setTimeout(doProcess, 20000);

Edit: if you cannot reverse the array for any reason just use next version

(function() {
   var arr = [...],
       len = arr.length;

   (function doProcess(i) {
       if (i) {
            console.log(len - i);
           /* do something with arr[len - i] */
           setTimeout(function() { doProcess(--i); }, 20000);

Here's some code I did for animating images using jQuery:

var enter = 500;
var show = 4000;
var exit = 300;
var direction1 = "right"; 
var direction2 = "left";
var logo = document.getElementById('Box1').getElementsByTagName('img');
var Num = $('#Box1 img').length;
var time_each = (enter+show+exit);
function startBox1(){
function Box1(x){
var buffer = time_each*x;
$(logo[x]).delay(buffer).show("slide", { direction: direction1 }, enter).delay(show).hide("slide", { direction: direction2 }, exit);

The trick was to set a buffer which equaled the time it took for each animation by the index of the current animation. The FOR loop runs each code immediately; the .delay() action and the buffer variable makes it appear as if each animation was happening one after the other. Then setInterval() recalls the FOR loop after every animation is complete. It restarts the process continuously.


You have to define a function, and inside the function it needs to set a timeout on itself. Like this:

var els = [1, 2, 3, 4, 5];

((function process_els(el_index) {
  var el = els[el_index];

  // do stuff to el here
  // do stuff to el above

  if (el_index + 1 < els.length) {
    setTimeout(function() { process_els(el_index + 1); }, 20000);


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