学习underscore源码整体架构，打造属于自己的函数式编程类库

_.chain([1, 2, 3]).reverse().value();
// => [3, 2, 1]

_.chain = function(obj) {
	var instance = _(obj);
	instance._chain = true;
	return instance;
};

var _ = function(obj) {
	if (obj instanceof _) return obj;
	if (!(this instanceof _)) return new _(obj);
	this._wrapped = obj;
};

var part1 = _.chain([1, 2, 3]);
var part2 = part1.reverse();
var part3 = part2.value();

// 没有后续part1.reverse()操作的情况下
console.log(part1); // {__wrapped: [1, 2, 3], _chain: true}

console.log(part2); // {__wrapped: [3, 2, 1], _chain: true}

console.log(part3); // [3, 2, 1]

_.chain([1,2,3]).reverse().value()s

var ArrayProto = Array.prototype;
// 遍历 数组 Array.prototype 的这些方法，赋值到 _.prototype 上
_.each([pop, push, reverse, shift, sort, splice, unshift], function(name) {
	// 这里的`method`是 reverse 函数
	var method = ArrayProto[name];
	_.prototype[name] = function() {
	// 这里的obj 就是数组 [1, 2, 3]
	var obj = this._wrapped;
	// arguments  是参数集合，指定reverse 的this指向为obj，参数为arguments， 并执行这个函数函数。执行后 obj 则是 [3, 2, 1]
	method.apply(obj, arguments);
	if ((name === shift || name === splice) && obj.length === 0) delete obj[0];
	// 重点在于这里 chainResult 函数。
	return chainResult(this, obj);
	};
});

// Helper function to continue chaining intermediate results.
var chainResult = function(instance, obj) {
	// 如果实例中有_chain 为 true 这个属性，则返回实例 支持链式调用的实例对象  { _chain: true, this._wrapped: [3, 2, 1] }，否则直接返回这个对象[3, 2, 1]。
	return instance._chain ? _(obj).chain() : obj;
};

_.prototype.value = function(){
	return this._wrapped;
}

_.prototype.toString = function() {
	return String(this._wrapped);
};

var String = function(){
	if(!(this instanceOf String)) return new String(obj);
}

var chainResult = function(instance, obj) {
	return instance._chain ? _(obj).chain() : obj;
};

_.mixin = function(obj) {
	// 遍历对象上的所有方法
	_.each(_.functions(obj), function(name) {
		// 比如 chain, obj[chain] 函数，自定义的，则赋值到_[name] 上，func 就是该函数。也就是说自定义的方法，不仅_函数对象上有，而且`_.prototype`上也有
	var func = _[name] = obj[name];
	_.prototype[name] = function() {
		// 处理的数据对象
		var args = [this._wrapped];
		// 处理的数据对象 和 arguments 结合
		push.apply(args, arguments);
		// 链式调用  chain.apply(_, args) 参数又被加上了 _chain属性，支持链式调用。
		// _.chain = function(obj) {
		//	var instance = _(obj);
		//	instance._chain = true;
		//	return instance;
		};
		return chainResult(this, func.apply(_, args));
	};
	});
	// 最终返回 _ 函数对象。
	return _;
};

_.mixin(_);

_.mixin({
	log: function(){
		console.log(哎呀，我被调用了);
	}
})
_.log() // 哎呀，我被调用了
_().log() // 哎呀，我被调用了

_.functions = _.methods = function(obj) {
	var names = [];
	for (var key in obj) {
	if (_.isFunction(obj[key])) names.push(key);
	}
	return names.sort();
};

var staticMethods = [];
var staticProperty = [];
for(var name in _){
	if(typeof _[name] === function){
		staticMethods.push(name);
	}
	else{
		staticProperty.push(name);
	}
}
console.log(staticProperty); // ["VERSION", "templateSettings"] 两个
console.log(staticMethods); // ["after", "all", "allKeys", "any", "assign", ...] 138个

var prototypeMethods = [];
var prototypeProperty = [];
for(var name in _.prototype){
	if(typeof _.prototype[name] === function){
		prototypeMethods.push(name);
	}
	else{
		prototypeProperty.push(name);
	}
}
console.log(prototypeProperty); // []
console.log(prototypeMethods); // ["after", "all", "allKeys", "any", "assign", ...] 152个

(function(){

}());

var root = typeof self == object && self.self === self && self ||
	typeof global == object && global.global === global && global ||
	this ||
	{};

if (typeof exports != undefined && !exports.nodeType) {
	if (typeof module != undefined && !module.nodeType && module.exports) {
	exports = module.exports = _;
	}
	exports._ = _;
} else {
	root._ = _;
}

if (typeof define == function && define.amd) {
	define(underscore, [], function() {
		return _;
	});
}

// 暂存在 root 上， 执行noConflict时再赋值回来
var previousUnderscore = root._;
_.noConflict = function() {
	root._ = previousUnderscore;
	return this;
};

(function() {
	var root = typeof self == object && self.self === self && self ||
		typeof global == object && global.global === global && global ||
		this ||
		{};
	var previousUnderscore = root._;

	var _ = function(obj) {
	  if (obj instanceof _) return obj;
	  if (!(this instanceof _)) return new _(obj);
	  this._wrapped = obj;
	};

	if (typeof exports != undefined && !exports.nodeType) {
	  if (typeof module != undefined && !module.nodeType && module.exports) {
		exports = module.exports = _;
	  }
	  exports._ = _;
	} else {
	  root._ = _;
	}
	_.VERSION = 1.9.1;

	_.chain = function(obj) {
	  var instance = _(obj);
	  instance._chain = true;
	  return instance;
	};

	var chainResult = function(instance, obj) {
	  return instance._chain ? _(obj).chain() : obj;
	};

	_.mixin = function(obj) {
	  _.each(_.functions(obj), function(name) {
		var func = _[name] = obj[name];
		_.prototype[name] = function() {
		  var args = [this._wrapped];
		  push.apply(args, arguments);
		  return chainResult(this, func.apply(_, args));
		};
	  });
	  return _;
	};

	_.mixin(_);

	_.each([pop, push, reverse, shift, sort, splice, unshift], function(name) {
	  var method = ArrayProto[name];
	  _.prototype[name] = function() {
		var obj = this._wrapped;
		method.apply(obj, arguments);
		if ((name === shift || name === splice) && obj.length === 0) delete obj[0];
		return chainResult(this, obj);
	  };
	});

	_.each([concat, join, slice], function(name) {
	  var method = ArrayProto[name];
	  _.prototype[name] = function() {
		return chainResult(this, method.apply(this._wrapped, arguments));
	  };
	});

	_.prototype.value = function() {
	  return this._wrapped;
	};

	_.prototype.valueOf = _.prototype.toJSON = _.prototype.value;

	_.prototype.toString = function() {
	  return String(this._wrapped);
	};

	if (typeof define == function && define.amd) {
	  define(underscore, [], function() {
		return _;
	  });
	}
}());