Ah! A homework question? Not really, a friend asked this on a group chat, but he asked us to solve it using functional programming.
The input should be an array such as [1, 2, 3, 5] and the output will be [2 - 1, 3 - 2, 5 - 3] === [1, 1, 2]
I solved it by using various built-in functions in Haskell, which are also available in lodash.
_.filter(_.map(_.zip(array, _.tail(array)), function (v) { return v[1] - v[0]; }));Try out the solution here: http://jsfiddle.net/debjitbis08/p2j02jf6/