For (i in array) vs for (i = 0;i<array.length;i++)

Question

Following a tutorial recently I noticed the use of both ways of using the for loop :
For (i in array) vs for (i = 0;i<array.length;i++)
but is there any difference between these?

Answer 1

in the second one you can access the index of the array (i) which might be very helpful in some situations

Answer 2

here is also forEach ...
and for of in ES6