Short coffeescript style question

Well I don't now coffeescript, but guess I can read it anyway :D

I think both are good and readable.
I don't know if you can add empty lines to the code. If you can:

strToCoordinates = (input) ->
    halves = input.split(',')
    if halves.length isnt 2
        console.log 'Please enter coordinates in format: x,y'; 
        return

    [x, y] = (parseFloat s for s in halves)
    unless isInteger(x) and isInteger(y)
        console.log 'The coordinates must be integers.'; 
        return

    if not inRange(x, y)
        console.log "Coordinates must be between 1 and #{GRID_SIZE}."; 
        return

    {x, y}

But this really is a minor arguable tweak (some will like it, some don't, I do).
Another point would be the "overuse" of returns. Functions are easier to read, if they do have lss return-statements. But Again, this usually applies to larger functions only.

I don't really like hiding the returns off the end of the line, so putting them on separate lines (or reverting to the original) would be preferable.

However, I'd also consider actually using postfix if. This would make the code read like this

strToCoordinates = (input) ->
    halves = input.split(',')
    return console.log 'Please enter coordinates in format: [x,y]' if halves.length isnt 2
    [x, y] = (parseFloat s for s in halves)
    return console.log 'The coordinates must be integers.' unless isInteger(x) and isInteger(y)
    return console.log "Coordinates must be between 1 and #{GRID_SIZE}." unless inRange(x, y)
    {x, y}

Under certain circumstances, postfix if can be buried at the end of the line. The presence of code straight after a return draws the eye to the conditions in this case. This would be my favoured way of writing the function as not only is it concise, it would be very easy to extend to extra conditions.

I would agree with the author's style just because it's not the absolute case.

If the author wants to build on the example and introduce more cases like a Z coordinate it's an else if statement, but your function you would have to have another inner if statement to handle there being three coordinates.

 if isnt 2 and 3 
      ...
      if 2 
        ...
      elseif 3

In this example you wouldn't be adding to it anyway since it's an excerise, but if it's code you want to use in a project then there's no telling what new requirements you might add in.

strToCoordinates = (input) ->
    [x, y] = (+z for z in (halves = input.split ',') if halves.length is 2)
    unless x isnt undefined and y isnt undefined then (console.log 'Input must be of the form `x, y`.'; return)
    unless x>>0 is x then (console.log "Each coordinate must be an integer."; return)
    unless inRange x - 1, y - 1 then (console.log "Each coordinate must be between 1 and #{GRID_SIZE}."; return)
    {x, y}

Just personally.