Getting the first and last element of an array in CoffeeScript

Question

If say I have an array and I would to iterate through the array, but do something different to the first and last element. How should I do that?

Taking the below code as example, how do I alert element a and e?

array = [a,b,c,d,e] for element in array   console.log(element) 

Thanks.

Answer 1

You can retrieve the first and last elements by using array destructuring with a splat:

[first, ..., last] = array 

This splat usage is supported in CoffeeScript >= 1.7.0.

Answer 2

The vanilla way of accessing the first and last element of an array is the same as in JS really: using the index 0 and length - 1:

console.log array[0], array[array.length - 1] 

CoffeeScript lets you write some nice array destructuring expressions:

[first, mid..., last] = array console.log first, last 

But i don't think it's worth it if you're not going to use the middle elements.

Underscore.js has some helper first and last methods that can make this more English-like (i don't want to use the phrase "self-explanatory" as i think any programmer would understand array indexing). They are easy to add to the Array objects if you don't want to use Underscore and you don't mind polluting the global namespace (this is what other libraries, like Sugar.js, do):

Array::first ?= (n) ->   if n? then @[0...(Math.max 0, n)] else @[0]  Array::last ?= (n) ->   if n? then @[(Math.max @length - n, 0)...] else @[@length - 1]  console.log array.first(), array.last() 

Update

This functions also allow you to get the n first or last elements in an array. If you don't need that functionality then the implementation would be much simpler (just the else branch basically).

Update 2

CoffeeScript >= 1.7 lets you write:

[first, ..., last] = array 

without generating an unnecessary array with the middle elements :D