What is the difference between for...in and for...of?

Can you explain the difference between for...in and for...of loops in JavaScript?

Sure! The for...in loop iterates over the keys of an object, while for...of iterates over the values of iterable objects like arrays.

Can you give me an example of each?

Of course! For for...in:

const obj = {a: 1, b: 2};
for (let key in obj) {
  console.log(key); // Outputs: a, b
}

For for...of:

const arr = [1, 2, 3];
for (let value of arr) {
  console.log(value); // Outputs: 1, 2, 3
}

Are there any performance differences between them?

Yes, generally, for...of is faster for arrays since it directly accesses the values, while for...in can be slower due to key lookups.

When should I use one over the other?

Use for...in when you need to iterate over object properties, and for...of when you want to iterate over array elements or other iterable objects.