Optimizing the number of loop iterations in JavaScript

In the following code, a programmer checks if the array contains the number 3:

let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
let exists = false;

for (let elem of arr) {
	if (elem === 3) {
		exists = true;
	}
}

console.log(exists);

What's wrong with his decision? It seems that no extra operations are done in the loop. The problem, however, is that after it is determined that the number 3 is in the array, the loop still continues to iterate until the end of the array.

It would be most irrational if the number 3 is found somewhere at the beginning of the array, and the array itself is, say, 1000 elements long. You get a thousand useless extra iterations of the loop! Not optimal.

We optimize code by stopping the loop in time:

let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
let exists = false;

for (let elem of arr) {
	if (elem === 3) {
		exists = true;
		break;
	}
}

console.log(exists);

The following code calculates how many array elements must be added to make the sum greater than 10. Perform optimization:

let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9];
let sum = 0;
let i = 1;

for (let elem of arr) {
	sum += elem;
	
	if (sum <= 10) {
		i++;
	}
}

console.log(i);

The following code outputs even numbers from a given range. Perform optimization:

for (let i = 0; i <= 100; i++) {
	if (i % 2 === 0) {
		console.log(i);
	}
}

The following code outputs numbers divisible by 2 and 3 at the same time. Perform optimization:

for (let i = 0; i <= 100; i++) {
	if (i % 2 === 0 && i % 3 === 0) {
		console.log(i);
	}
}

The following code searches for all Fridays the 13th in the current year. Perform optimization:

for (let i = 0; i <= 11; i++) {
	let curr = new Date;
	let last = new Date(curr.getFullYear(), i + 1, 0).getDate();
	
	for (let j = 1; j <= last; j++) {
		let date = new Date(curr.getFullYear(), i, j);
		
		if (date.getDate() === 13 && date.getDay() === 5) {
			console.log(date);
		}
	}
}