1_mixin.coffee

mixin DumbEqualsOperand
  equals: (other) ->
    this == other

class MyClass implements DumbEqualsOperand

m = new MyClass
n = new MyClass
console.log(m.equals n)
  

2_mixin.js

(function(){
  var DumbEqualsOperand, MyClass, m, n;
  var __hasProp = Object.prototype.hasOwnProperty, __implements = function(child, mixin) {
    for (var key in mixin) { if (__hasProp.call(mixin, key)) child[key] = mixin[key]; }
  };
  // there's actually no reason to implement mixins as classes instead of simple hashes as far as I can tell, but am doing so for consistency
  DumbEqualsOperand = function(){
    function DumbEqualsOperand(){}
    DumbEqualsOperand.prototype.equals = function(other){
      return this == other;
    };
    return DumbEqualsOperand;
  }();
  MyClass = function(){
    MyClass = function(){};
    _implements(MyClass, DumbEqualsOperand);
  }();

  m = new MyClass();
  n = new MyClass();
  console.log(m.equals(n));
}).call(this);

3_exceptions.js

function BaseError(){}

function AnnoyingError(){}
AnnoyingError.prototype = BaseError;

function BothersomeError(){}
BothersomeError.prototype = BaseError;


function errorProne(idx){
  if(idx < 0){
    throw new AnnoyingError();
  } else if(idx > 1){
    throw new BothersomeError();
  }
}

try {
  errorProne(-2);
} catch(e){
  if(e instanceof AnnoyingError){
    console.log("that was annoying");
  } else if(e instanceof BothersomeError){
    console.log("that was bothersome");
  }
}