Question

What is the output?

const myLifeSummedUp = ['☕', '', '', ''];

for (let item in myLifeSummedUp) {
  console.log(item);
}

for (let item of myLifeSummedUp) {
  console.log(item);
}

• A: 0 1 2 3 and "☕" "" "" ""
• B: "☕" "" "" "" and "☕" "" "" ""
• C: "☕" "" "" "" and 0 1 2 3
• D: 0 1 2 3 and {0: "☕", 1: "", 2: "", 3: ""}

Answer 1

Answer: A

With a for-in loop, we can iterate over enumerable properties. In an array, the enumerable properties are the "keys" of array elements, which are actually their indexes. You could see an array as:

{0: "☕", 1: "", 2: "", 3: ""}

Where the keys are the enumerable properties. 0 1 2 3 get logged.

With a for-of loop, we can iterate over iterables. An array is an iterable. When we iterate over the array, the variable "item" is equal to the element it's currently iterating over, "☕" "" "" "" get logged.