它做五件事：
- 它创建一个新对象。这个对象的类型就是 object 。
- 它将这个新对象的内部不可访问的 [[prototype]] （即 proto ）属性设置为构造函数的外部可访问 原型 对象（每个函数对象都会自动具有 prototype 属性）。
- 它使
this
变量指向新创建的对象。 - 每当
this
提及时，它都会使用新创建的对象执行构造函数。 - 除非构造函数返回非
null
对象引用，否则它将返回新创建的对象。在这种情况下，将返回该对象引用。
注意： 构造函数 是指
new关键字后面的函数，如
new ConstructorFunction(arg1, arg2)
完成此操作后，如果请求新对象的未定义属性，则脚本将改为检查对象的 [[prototype]]
对象的属性。这就是您可以获得类似于Javascript中传统类继承的方式的方法。
关于这一点，最困难的部分是点号2。每个对象（包括函数）都具有称为 [[prototype]]的 内部属性。它可以 只
被在创建对象的时间与设置，无论是 新的 ，具有 的Object.create
，或者基于文本（函数默认Function.prototype的，数字到Number.prototype等）。只能使用
Object.getPrototypeOf（someObject） 读取它。有 没有 其他的方式来设置或读取此值。
除了隐藏的 [[prototype]] 属性外，函数还具有一个称为 prototype
的属性，您可以访问和修改此属性，以为您创建的对象提供继承的属性和方法。
这是一个例子：
ObjMaker = function() {this.a = 'first';};// ObjMaker is just a function, there's nothing special about it that makes // it a constructor.ObjMaker.prototype.b = 'second';// like all functions, ObjMaker has an accessible prototype property that // we can alter. I just added a property called 'b' to it. Like // all objects, ObjMaker also has an inaccessible [[prototype]] property// that we can't do anything withobj1 = new ObjMaker();// 3 things just happened.// A new, empty object was created called obj1. At first obj1 was the same// as {}. The [[prototype]] property of obj1 was then set to the current// object value of the ObjMaker.prototype (if ObjMaker.prototype is later// assigned a new object value, obj1's [[prototype]] will not change, but you// can alter the properties of ObjMaker.prototype to add to both the// prototype and [[prototype]]). The ObjMaker function was executed, with// obj1 in place of this... so obj1.a was set to 'first'.obj1.a;// returns 'first'obj1.b;// obj1 doesn't have a property called 'b', so Javascript checks // its [[prototype]]. Its [[prototype]] is the same as ObjMaker.prototype// ObjMaker.prototype has a property called 'b' with value 'second'// returns 'second'就像类继承一样，因为现在，您使用的任何对象
new ObjMaker()也似乎都继承了’b’属性。
如果您想要子类之类的东西，请执行以下操作：
SubObjMaker = function () {};SubObjMaker.prototype = new ObjMaker(); // note: this pattern is deprecated!// Because we used 'new', the [[prototype]] property of SubObjMaker.prototype// is now set to the object value of ObjMaker.prototype.// The modern way to do this is with Object.create(), which was added in ECMAscript 5:// SubObjMaker.prototype = Object.create(ObjMaker.prototype);SubObjMaker.prototype.c = 'third'; obj2 = new SubObjMaker();// [[prototype]] property of obj2 is now set to SubObjMaker.prototype// Remember that the [[prototype]] property of SubObjMaker.prototype// is ObjMaker.prototype. So now obj2 has a prototype chain!// obj2 ---> SubObjMaker.prototype ---> ObjMaker.prototypeobj2.c;// returns 'third', from SubObjMaker.prototypeobj2.b;// returns 'second', from ObjMaker.prototypeobj2.a;// returns 'first', from SubObjMaker.prototype, because SubObjMaker.prototype // was created with the ObjMaker function, which assigned a for us
