// Underscore骨骼  
(function () { var root \= this; var breaker \= {}; var ArrayProto \= Array.prototype, ObjProto \= Object.prototype; var nativeForEach \= ArrayProto.forEach,  nativeMap \= ArrayProto.map,  nativeFilter \= ArrayProto.filter,  nativeKeys \= Object.keys; var slice \= ArrayProto.slice,  unshift \= ArrayProto.unshift,  hasOwnProperty \= ObjProto.hasOwnProperty; // 构造函数  var \_ \= function (obj) { return new wrapper(obj); }; // 向全局暴露接口  root.\_ \= \_; // 类型检测  \_.isNumber \= function (obj) { return !!(obj \=== 0 || (obj && obj.toExponential && obj.toFixed));  };  \_.isFunction \= function (obj) { return !!(obj && obj.constructor && obj.call && obj.apply);  }; // 遍历扩展  var each \= \_.each \= \_.forEach \= function (obj, iterator, context) { if (obj \=== null) return; if (nativeForEach && obj.forEach \=== nativeForEach) {  obj.forEach(iterator, context);  } else if (\_.isNumber(obj.length)) { for (var i \= 0, l \= obj.length; i < l; i++) { if (iterator.call(context, obj\[i\], i, obj) \=== breaker) return;   }  } else { for (var key in obj) { if (hasOwnProperty.call(obj, key)) { if (iterator.call(context, obj\[key\], key, obj) \=== breaker) return;   }   }  }  }; // 返回对象上面的函数名  \_.functions \= \_.methods \= function (obj) { return \_.filter(\_.keys(obj), function (key) { return \_.isFunction(obj\[key\])}).sort();  }; // 过滤数组  \_.filter \= \_.select \= function (obj, iterator, context) { var results \= \[\]; if (obj \== null) return results; if (nativeFilter && obj.filter \=== nativeFilter) return obj.filter(iterator, context);  each(obj, function (value, index, list) { if (iterator.call(context, value, index, list)) results\[results.length\] \= value;   }); return results;  }; // 获取key值  \_.keys \= nativeKeys || function (obj) { if (obj !== Object(obj)) throw new TypeError('Invalid object'); var keys \= \[\]; for (var key in obj) if (hasOwnProperty.call(obj, key)) keys\[keys.length\] \= key; return keys;  }; // 用于实验的map方法  \_.map \= function (obj, iterator, context) { var results \= \[\]; if (obj \== null) return results; if (nativeMap && obj.map \=== nativeMap) return obj.map(iterator, context);  each(obj, function (value, index, list) {  results\[results.length\] \= iterator.call(context, value, index, list);  }); return results;  }; // 链式操作主要部分  var wrapper \= function (obj) { this.\_wrapped \= obj; };  \_.prototype \= wrapper.prototype; // 扩展自定义方法到Wrap包装器上  \_.mixin \= function (obj) {  each(\_.functions(obj), function (name) {  addToWrapper(name, \_\[name\] \= obj\[name\]);  });  }; // 是否对结果进行链式包装返回  var result \= function (obj, chain) { return chain ? \_(obj).chain() : obj;  }; // 将方法扩展到包装器的原型上  var addToWrapper \= function (name, func) {  wrapper.prototype\[name\] \= function () { var args \= slice.call(arguments);  unshift.call(args, this.\_wrapped); return result(func.apply(\_, args), this.\_chain);  };  }; // 将所有Underscore上的方法添加到Wrap包装器上  \_.mixin(\_); // 扩展Array上的方法到wrap包装器上-包装原数组  each(\['pop', 'push', 'reverse', 'shift', 'sort', 'splice', 'unshift'\], function (name) { var method \= ArrayProto\[name\];  wrapper.prototype\[name\] \= function () {  method.apply(this.\_wrapped, arguments); return result(this.\_wrapped, this.\_chain);  };  }); // 扩展Array上的方法到wrap包装器上-包装返回值  each(\['concat', 'join', 'slice'\], function (name) { var method \= ArrayProto\[name\];  wrapper.prototype\[name\] \= function () { return result(method.apply(this.\_wrapped, arguments), this.\_chain);  };  }); // 添加链式方法的实现  wrapper.prototype.chain \= function () { this.\_chain \= true; return this;  }; // 提取链式包装的内容  wrapper.prototype.value \= function () { return this.\_wrapped;  };  })();  // 结果测试 步骤：将数组\[1,2,3\]进行链式包装，然后将其用val \* 2来map，紧接着用filter进行val < 5过滤,   
// 然后pop,concat最后获取其值value  
var re \= \_(\[1,2,3\]).chain().map(function (val) { return val \* 2;  
}).filter(function (val) { return val < 5;  
}).pop().concat(\['5'\]).value();  alert(re);