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I have a build chain setup that will convert a file from coffeescript to typescript to javascript. My question is: what is the most minimally intrusive way to add type signatures to a coffeescript function?

coffeescript supports raw javascript through backticks. However, that means coffeescript no longer understands the backtick snippet.

Coffeescript rejects these:

f = (`a:String`) -> a + 2
f = (a`:String`) -> a + 2

I can write this above the function:

`var f = (String) => any`

It compiles, but does not do the type-checking. I think this is because Coffeescript already declared the variable.

The only way I could figure out how to make it work requires a lot of boilerplate

f = (a) ->
  `return (function(a:String){`
  a + 2;
  `})(a)`

Backticks do not seem to work properly in the new Coffeescript Redux compiler: https://github.com/michaelficarra/CoffeeScriptRedux/issues/71

I am well aware that this is a dubious endeavor, it is just an experiement right now. I currently use contracts.coffee, but I am looking for actual types.

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    Perhaps you should choose one language or the other. Your code reminds of misguided Pascal programmers doing #define BEGIN { when programming C. Commented Oct 13, 2012 at 18:13
  • 3
    This does not seem like a good idea... Commented Oct 24, 2012 at 22:43
  • 1
    You two previous commenters, obviously mixing the two like that is hideous. I believe that is why the OP is asking, and would like a solution... Commented Jan 16, 2018 at 0:35

4 Answers 4

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21

Here's my project which transpiles CoffeeScript into TypeScript and then merges it with a d.ts file containing types. Then reports compilation errors, if any.

Its called Compiled-Coffee.

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1 Comment

It should be called ToffeeScript
17

If you want to write CoffeeScript, it is best to write CoffeeScript and compile to JavaScript.

The benefit of TypeScript is mostly design-time benefit and better tooling, so using it in the middle of CoffeeScript and JavaScript adds very little benefit as you will get design time and tooling based on your CoffeeScript code.

You can consume the libraries you write in CoffeeScript in TypeScript and vice-versa, so you can maintain your CoffeeScript libraries in CoffeeScript and consume them in your new TypeScript files while you decide which way to go.

Update: I'm not sure how there can be such a wide misinterpretation of this answer - I'm going to assume that I haven't explained this well (rather than assuming it is merely straw-man argument or hyper-sensitivity to language comparison).

TypeScript is indeed a type system for JavaScript. Static types are more use to you as a programmer earlier in the workflow. Having design-time warnings in your IDE means rapid correction of common errors like mis-typed variable names, incorrect parameters, invalid operations and a whole lot more. Having code underlined and annotated with an error means instant feedback. Having this at compile-time is good, but your feedback loop is longer. I won't even talk about run-time given that all types are erased by this point when using TypeScript.

As to all the "TypeScript vs CoffeeScript" comments - this question is not about that at all. The question is about compiling from CoffeeScript to TypeScript and then to JavaScript. Let's look at why this might not be ideal:

  • You will only get type feedback at compile time
  • You won't get auto-completion
  • Your CoffeeScript code will no longer be compact - it will have type annotations
  • Your CoffeeScript code will no longer be valid without your intermediate compiler
  • You will have to use an additional compiler and it will need to be in-step with CoffeeScript version x and TypeScript version y
  • Your IDE won't understand your CoffeeScript code
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10 Comments

Not sure how types are not one of the major benefits of TypeScript. Have you used it?
@GregWeber types are indeed a benefit, but primarily at design time. If your design time was CoffeeScript, which was compiled into TypeScript, the benefit of type checking would be greatly reduced as you would only know about the error when TypeScript compiled to JavaScript. The philosophy of TypeScript is to bring better tooling to the design-time to make developers more productive.
@GregWeber this is a useful video in which Anders Hejlsberg explains this point, probably better than I can - channel9.msdn.com/posts/…
Greg is right. Types are, IMHO as a vim user, the principle benefit of TypeScript. Note that this can be true even if the language authors did not intend it to be.
@GregWeber Types are the primary benefit of TypeScript; the primary benefit of types in this case is the improved tooling. All type information is lost by the time you get to JavaScript. Even if you declare functions in back ticks in CoffeeScript, you won't get any type checking if you call those functions from CoffeeScript.
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I think what I came up with is the best I can do. Things are harder in the new Coffeescript Redux compiler: it would actually be easier to try to hack the current coffeescript compiler to make this work.

The way of making this look less hacky is:

`var f : (a:Number) => Number = originalF`

However, typescript's weak type inference doesn't do that well with this form. This gets proper type analysis:

f = (a) ->
  `var a : Number = a`
  a + 2

However, I am still not sure how to specify a return value with this form.

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Comments

2

Typescript is a strong type javascript. Coffee-script provides a more comfortable way of writing and reading. I do not treat coffee-script as a language. It's just a way, a style that can be attached to any language: Coffee Style Smart Computer Language should be the future

It's very ugly and stupid through backtick to 'support' the such strong type. The correct way to implement the coffee-script with strong type:

  • Modify the CoffeeScriptRedux source to add the strong type supported
  • Modify the Typescript parser source to use coffee-script syntax.
    • It seems nobody do this.
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1 Comment

I wish some could do the last one, to allow some coffescripty syntax in TypeScript :-)

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