Splitting an array using coffeescript, what is _ref?

Question

In CoffeeScript docs for splicing arrays , what is the purpose of the final , _ref ?

CoffeeScript:

 numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] numbers[3..6] = [-3, -4, -5, -6] 

Compiles:

 var numbers, _ref; numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]; [].splice.apply(numbers, [3, 4].concat(_ref = [-3, -4, -5, -6])), _ref; 

Answer 1

This is because the CoffeeScript cut operation wants to return the newly selected slice, but splice () returns the deleted items.

So, to achieve this, he compiles the construct into a piece of code that first assigns a slice to the local variable _ref , and then uses a comma to return this variable after calling splice() .