for-in-for-of-forEach.js

/// ----> for in

const array = [1, 2, 3, 4, 5, 6, 7, 8];

for (let prop in ["1", "b", "c", "d"]) {
  console.log(prop); // 0,1,2,3 array indexes
}

for (let prop in "string") {
  console.log(prop); // 0,1,2,3,4,5 string indexes
}

for (let prop in { a: 1, b: 2, c: 3 }) {
  console.log(prop); // a,b,c  (object property names)
}

for (let prop in new Set(["a", "b", "c", d])) {
  console.log(prop); // undefined (no enumerable properties)
}

// ------> for of

for (let val of ["a", "b", "c"]) console.log(val); // a, b, c (array values)

for (let val of "str") console.log(val); // s, t, r (string characters)

for (let val of { a: 1, b: 2, c: 3 }) console.log(prop); // TypeError (not iterable)

for (let val of new Set(["a", "b", "a", "d"])) console.log(val); // a, b, d (Set values)

////// ----> for each

["a", "b", "c"].forEach(
  (val) => console.log(val) // a, b, c (array values)
);

["a", "b", "c"].forEach(
  (val, i) => console.log(i) // 0, 1, 2 (array indexes)
);