Join operates on an array, takes a specified delimiter and returns a string.
Split Operates on a string. The first argument is the specified delimiter and returns an array. The first argument is not included in the array and the second argument is the array length. If the second parameter is set to 4, the array is still 3 in length and will not be filled.
Slice operates on an array, truncating it with the first argument being the start index and the second argument being the one before the end index (by default, the last one), and returns the truncated array unchanged
Splice operates on the array. The first argument is where the deletion started, the second argument is the number of deletions, and the third argument is the element added (the element is added before the deletion started). The original array will change