Underscore doesn't work in Coffeescript's console

Question

I've just started using Coffeescript and the Coffeescript console, and Underscore. However, whenever I define a function, Coffeescript decides that `_` means that function, and seems to forget the initial assignment of `_ = require 'underscore'`. Why does this happen? How can I prevent it? (I'd really like to be able to copy paste code from my files into the console.) (Does `_` have some special meaning in the Coffeescript console? Does it mean "the last result" or something? That'd explain my issue?) Details: ``` $ coffee coffee> _.contains [1, 2, 3], 3 # no Underscore, initially TypeError: Cannot call method 'contains' of undefined at ... coffee> coffee> _ = require 'underscore' { [Function] _: [Circular], VERSION: '1.3.3', forEach: [Function], ... coffee> _.contains [1, 2, 3], 3 # now Underscore works fine true coffee> ------> someFunction = (a, b) -> # define a function ... ......> a + b [Function] coffee> coffee> _.contains [1, 2, 3], 3 # now `_` is not Underscore any more! TypeE…

Accepted Answer

The CoffeeScript REPL has this JavaScript at its heart:

```
try {
  _ = global._;
  returnValue = CoffeeScript["eval"]("_=(" + code + "
)", {
    filename: 'repl',
    modulename: 'repl'
  });
  if (returnValue === void 0) {
    global._ = _;
  }
  repl.output.write("" + (inspect(returnValue, false, 2, enableColours)) + "
");
} catch (err) {
  error(err);
}
```

So if the last command returned something then `_` will be that something. I can't find any documentation about this though but searching for `_` isn't a terribly productive activity. If you want to use Underscore.js in the CoffeeScript REPL, you'll have to call it something other than `_`.

Thanks to Trevor Burnham (who wrote the book so I think we can trust him on this) we know that the CoffeeScript REPL uses `_` as the last result to match the behavior of the node.js REPL:

REPL Features [...] The special variable `_` (underscore) contains the result of the last expression.

Ruby's `irb` does the same thing.

Underscore doesn't work in Coffeescript's console

Solution

Problem