Which loop is faster?

In modern JavaScript, the difference in speed between for, while, and for..of is extremely small for most tasks. If you only have 1000 elements in an array, you won't notice the difference.

1. Classical for

The fastest, as the V8 engine (in Chrome and Node.js) has been honing its optimization for decades.

2. for..of

The gold standard for readability. It's slightly slower than a classic for, but in 99% of cases, this isn't critical.

3. for..in — DANGER

This loop was created for iterating over OBJECT properties. When working with an array, it:

1. Is 10-50 times slower than the others.
2. Iterates over properties out of order.
3. Might pick up extra properties from prototypes.