Question

These two functions, _.forEach and $.each, taken respectively from underscore and jQuery seems to make the same thing.

What are the possible reasons to prefer one implementation to the other?

Answer 1

_.forEach and $.each differs for the arguments passed to the callback.

If you use _.forEach, the first argument passed to the callback is the value, not the key.
So if you don’t bother at all about the key you should use _.forEach.

Other differences:

1. _.forEach it will be a bit faster as it uses the native Arrray.prototype.forEach in modern browsers.
2. the this value is also different. jQuery’s behavior doesn’t follow the standard, underscore’s does.