Converting from CoffeeScript - caffeine-suite/caffeine-script GitHub Wiki

Related: Coming from CoffeeScript

Classes

CaffeineScript uses ES6 classes. CoffeeScript 1.x classes CANNOT EXTEND ES6 CLASSES. But, ES6 classes CAN extend CoffeeScript classes. So, as you convert your CoffeeScript, start with the leaf-node classes, classes which are not extended, and then work your way up the inheritance tree.

Semantic Changes

Compiles, but means something different.

• foo bar: 1, 2 is interpreted as foo({bar: [1, 2]}); in CaffeineScript

Tail comprehensions are gone.

value + 1 array value in myArray

# note above line is interpreted as
value + [1, array value in myArray with value]

# Use instead:
array value in myArray with value + 1

Syntactic Changes

Won't compile.

• for ... in/of is gone. Replace 'for' with 'each', or array, depending on what you want the return value to be. The iteration type, 'in' vs 'of', is detected at runtime.

I have tentative plans for optionally specifying the iteration type for increased runtime performance, but I want to see a concrete example where performance is a problem.

Blocks are more strict. Once you start a block, any de-indentation ends the block:

#CoffeeScript
# this pattern no longer works:
foo ->
  a
,
  b

# Block-method-invocation solves
# a lot of these problems nicely:
foo
  -> a
  b

Gotchas

As I convert my code bases from CoffeeScript to CaffeineScript, I'm making notes on what tripped me up.

• When converting to word strings, make sure to remove end-quote.
• array/object/find/each keywords are syntactically very flexible in CaffeineScript, so often existing code will still compile by work very differently, if at all, if these were in the original CoffeeScript.
• All """, ''', ### and /// CoffeeScript brackets need to be fixed manually.
• 'when' clause and scoping. Right now the 'when' clause is in its own scope. Assigning a new variable in a 'when' clause will NOT be shared with the with-clause. This is a bug.
• Coffee:for key, value of myObject ... vs Caffeine:array value, key in myObject ... The order of comprehension-variables is swapped for object iteration. In caffeine-script we prefer consistency: the value always is first, the key always is second, regardless if it is an array or object iteration.

CoffeeScript's WontFixs

The main reason I started from scratch, rather than contribute or fork CoffeeScript, is that some of the biggest problems CaffeineScript fixes are categorized as 'wontfix' in CoffeeScript:

• Block invocation

  • https://github.com/jashkenas/coffeescript/issues/575#issuecomment-349631
  • https://github.com/jashkenas/coffeescript/issues/1549
  • https://github.com/jashkenas/coffeescript/issues/3114

• Array Block Syntax / Implicit Arrays

  • implicit arrays

• Going beyond 'just javascript'

  • operator overloading

NOTES: 
(foo, bar = 132) ->
.length == 1 # CaffieneScript & ES6 & probably CoffeeScriptV2
# This is ES6's definition for length. Personally, I hate it, it should be 2, but CaffeineScript is currently Es6-compatible on this. I may be changing CaffeineScript to CoffeeScriptV1's semantics:
# CoffeeScriptV1, .length == 2
# Why does this matter? The biggest problem is adding or removing defaults should NOT effect the API (i.e. change externally introspect-able things like .length)

Object.keys class Foo
  @bar: ->
== bar: -> # only CaffeineScript and CoffeeScript V1
# ES6 and CoffeeScriptV2 get this wrong, but we get it right. Class members ARE enumerable.