JavaScript’s Array.prototype.forEach is usually significantly slower than a for loop. This is because forEach includes extra checks that a for loop normally doesn’t have. Are there any cases where a forEach loop works (because of these checks) where a for loop doesn’t?
To be clear, I am not asking why for is faster than forEach. I am asking if the extra checks in forEach are ever useful.
There are several differences between forEach and using a for loop
The most obvious is how they deal with sparse arrays. forEach wont try to run the callback if it hits an empty array element but for will and the array item will give undefined.
On the other side, you can’t just break out of a forEach as you can a for loop.
See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach for further details.
You could make the for loop as slow as you want by changing the traditional increment to a more complex operation. It also has to do an inequality check during each iteration, so that is another opportunity to introduce delays, by using a more complex condition.
forEach is very specific, but for can offer more flexibility.
