Detect last iteration in FOR OF loop in ES6 javascript

Question

There are multiple ways of finding out the last iteration of a for and for...in loop. But how do I find the last iteration in a for...of loop. I could not find that in the documentation.

for (item of array) {     if (detect_last_iteration_here) {         do_not_do_something     } } 

Answer 1

One approach is using Array.prototype.entries():

for (const [i, value] of arr.entries()) {     if (i === arr.length - 1) {         // do your thing     } } 

Another way is keeping a count outside the loop like Shidersz suggested. I don't think you want to check indexOf(item) though because that poses a problem if the last item is duplicated somewhere else in the array...

Answer 2

One possible way is to initialize a counter outside the loop, and decrement it on every iteration:

const data = [1, 2, 3]; let iterations = data.length;  for (item of data) {     if (!--iterations)         console.log(item + " => This is the last iteration...");     else         console.log(item); }

.as-console {background-color:black !important; color:lime;} .as-console-wrapper {max-height:100% !important; top:0;}

Note that !--iterations is evaluated as !(--iterations) and the expression will be true when iterations=1.