Underscore在Coffeescript的控制台中不起作用

Question

我刚刚开始使用Coffeescript和Coffeescript控制台,以及Underscore.但是,每当我定义一个函数时,Coffeescript就决定了_那个函数,并且似乎忘记了初始赋值_ = require 'underscore'.

为什么会这样？我该怎样预防呢？
(我真的希望能够将我的文件中的粘贴代码复制到控制台中.)

(_在Coffeescript控制台中有一些特殊含义吗？它是指"最后的结果"还是什么？这可以解释我的问题吗？)

细节:

$ 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!
TypeError: Object function (a, b) {    # Does `_` mean "last result" or sth?
  return a + b;
} has no method 'contains'
    at evalmachine.<anonymous>:3:7
    at Object.eval (/usr/local/lib/node_modules/coffee-script/lib/coffee-script/coffee-script.js:142:17)
    at Interface.<anonymous> (/usr/local/lib/node_modules/coffee-script/lib/coffee-script/repl.js:131:40)
    at Interface.emit (events.js:67:17)
    at Interface._onLine (readline.js:162:10)
    at Interface._line (readline.js:426:8)
    at Interface._ttyWrite (readline.js:603:14)
    at ReadStream.<anonymous> (readline.js:82:12)
    at ReadStream.emit (events.js:88:20)
    at ReadStream._emitKey (tty.js:327:10)
coffee> 
coffee> _ = require 'underscore'
coffee> _.contains [1, 2, 3], 3    # Now all is fine again, for a short while
true

Answer 1

CoffeeScript REPL的核心是这个JavaScript:

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

因此,如果最后一个命令返回了什么,那么_就是那个东西.我找不到任何关于此的文档,但搜索_并不是一项非常有成效的活动.如果你想在CoffeeScript REPL中使用Underscore.js,你必须把它称为其他东西_.

感谢Trevor Burnham(我写这本书所以我认为我们可以相信他)我们知道CoffeeScript REPL使用_最后的结果来匹配node.js REPL的行为:

REPL Features
[...]
特殊变量_(下划线)包含最后一个表达式的结果.

Ruby irb也做同样的事情.