JuniorTheoryCommon

What does the program print?

JavaScript

const letters = ["x", "y"];
let out = "";
for (const i in letters) {
    out += i;
}
for (const ch of letters) {
    out += ch;
}
console.log(out);

01xy

Expecting for…in to give the elements: over an array it gives the indexes as strings, "0" and "1"; the elements come from for…of.
Expecting the indexes to start at 1: array indexes start at 0, so the two elements of letters have the indexes 0 and 1.

JuniorTheoryCommon

JavaScript

const letters = ["x", "y"];
let out = "";
for (const i in letters) {
    out += i;
}
for (const ch of letters) {
    out += ch;
}
console.log(out);

01xy

Expecting for…in to give the elements: over an array it gives the indexes as strings, "0" and "1"; the elements come from for…of.
Expecting the indexes to start at 1: array indexes start at 0, so the two elements of letters have the indexes 0 and 1.