Underscore 1.3.3 http://documentcloud.github.com/underscore/
Underscore.js Version (1.2.3) 中文文档 http://www.css88.com/doc/underscore/
Underscore Reference http://autotelicum.github.com/Smooth-CoffeeScript/literate/underscore.html

https://github.com/documentcloud/underscore/blob/master/underscore.js
https://github.com/jashkenas/coffee-script/blob/master/examples/underscore.coffee
underscore.coffee http://coffeescript.org/documentation/docs/underscore.html
underscore.js http://documentcloud.github.com/underscore/docs/underscore.html

代码和注释反正到处都有, 郁闷就是原型继承没学好…
求问源码里的 prototype .call .apply 怎样理解, 还有看什么(关于原型)教程?

— 更新

_.map = (obj, iterator, context) ->
  if nativeMap and obj.map is nativeMap
    return obj.map(iterator, context)
  results = []
  _.each obj, (value, index, list) ->
    results.push iterator.call context, value, index, list
  results

比如这里的 context, 手册上 .call 说这个是:

The value of this provided for the call to fun. Note that this may not be the actual value seen by the method: if the method is a function in non-strict mode code, null and undefined will be replaced with the global object, and primitive values will be boxed.
.map 里面说是:
Object to use as this when executing callback.

那 context 变量在这里有什么作用呢? 实际遇到的情况是什么样子的?

还有 nativeFilter 相似的方法, 为什么需要两次确认? if nativeFilter and obj.filter is nativeFilter