JuniorTheoryCommon

What does the program print?

JavaScript

const fns = [];
for (var i = 0; i < 3; i++) {
    fns.push(() => i);
}
console.log(fns[0](), fns[1](), fns[2]());

3 3 3

Expecting 0 1 2: with var there is one i for the whole loop, and the functions read it when they are called, after the loop; only let gives each iteration its own i.
Expecting 2 2 2: the loop stops only when i < 3 is false, so after the last iteration i++ makes it 3.

JuniorTheoryCommon

JavaScript

const fns = [];
for (var i = 0; i < 3; i++) {
    fns.push(() => i);
}
console.log(fns[0](), fns[1](), fns[2]());

3 3 3

Expecting 0 1 2: with var there is one i for the whole loop, and the functions read it when they are called, after the loop; only let gives each iteration its own i.
Expecting 2 2 2: the loop stops only when i < 3 is false, so after the last iteration i++ makes it 3.