REPL changes context on each evaluation

[TrevorBurnham]

A helpful reader of my book just reported an interesting issue. Michael, maybe you can figure this one out?

coffee> this is global
true  # as expected
coffee> foo = -> this is global
coffee> foo()
false  # surprising...
coffee> foo.call global
false  # mind-blowing

And it's not that functions can't be run in any context; it seems they just can't be run in global:

coffee> bar = {}
coffee> baz = -> this is bar
coffee> baz.call bar
true

Here's another rub: If you define and run the function all in one line, then it does run in the global context by default:

coffee> (-> this is global)()
true
coffee> (-> this is global).call global
true
coffee> do testFunc = -> this is global
true

Tested under CoffeeScript 1.1.1 and current master. Any ideas?

Btw, tested under the Node REPL; no issues there:

node> var foo = function() {console.log(this === global);}
node> foo()
true

[michaelficarra]

Yeah, the REPL has some issues with global objects currently, likely all my fault. See #1425 and #1035 for the others. These three are on the top of my TODO list, but it could be up to a week before I get enough time to actually sit down and figure these out.

edit: Actually, I'll probably get to them tomorrow.

edit: Actually, probably not... ugh.

[telemachus]

For what it's worth, I'm getting varied and inconsistent results for coffee, node and v8 (using the REPL and interpreter for all three): https://gist.github.com/1033081

[TrevorBurnham]

@telemachus I posted an answer to your Stack Overflow question: http://stackoverflow.com/questions/6396467/a-puzzle-about-this-in-javascript-coffeescript/6397029#6397029

The inconsistency is because this in the outermost scope is global under v8 and the REPL, but exports under coffee and node when a file is being run. That's all as it should be; I need to explain it better in the book.

[satyr]

Renamed title. ("Function context can't be global in REPL" was inaccurate.)

[michaelficarra]

Check this out:

self = do -> this
self is global # true!

@TrevorBurnham: After playing around with this for a while, I'm pretty sure you've found a bug with node's vm.runInNewContext.

vm = require('vm');
sandbox = {};
sandbox.global = sandbox;
vm.runInNewContext('global === this', sandbox); // true, as expected
vm.runInNewContext('(function(){ return global === this }())', sandbox); // true, as expected
vm.runInNewContext('var fn = function(){ return global === this }', sandbox);
vm.runInNewContext('fn()', sandbox); // false, unexpectedly

I'll post back here with the issue number as soon as I file it.

update: See node issue #1280.

[michaelficarra]

Fixed by fff4c9c, which doesn't use vm.runInNewContext

[satyr]

Should probably fix tab completion as well.

$ node
> Array.foo = 0
0
> Array.f

Hitting tab here completes to .foo as expected. Not the case for coffee REPL.

[michaelficarra]

@satyr: Fixed tab completion in af1cf34