js-new、object.create、bind的模拟实现【转载备忘】

//创建Person构造函数，参数为name,age
function Person(name,age){
    this.name = name;
    this.age = age;
}
 
function _new(){
    //1.拿到传入的参数中的第一个参数，即构造函数名Func
    var Func = [].shift.call(arguments);
    //2.创建一个空对象obj,并让其继承Func.prototype
    var obj = Object.create(Func.prototype);
    //3.执行构造函数，并将this指向创建的空对象obj
    Func.apply(obj,arguments)
    //4.返回创建的对象obj
    return obj
}
 
 
xm = _new(Person,'xiaoming',18);
 
console.log(xm);

来源https://blog.csdn.net/u010342862/article/details/80016695

 

if (typeof Object.create !== "function") {
    Object.create = function (proto, propertiesObject) {
        if (typeof proto !== 'object' && typeof proto !== 'function') {
            throw new TypeError('Object prototype may only be an Object: ' + proto);
        } else if (proto === null) {
            throw new Error("This browser's implementation of Object.create is a shim and doesn't support 'null' as the first argument.");
        }

        if (typeof propertiesObject != 'undefined') throw new Error("This browser's implementation of Object.create is a shim and doesn't support a second argument.");

        function F() {}
        F.prototype = proto;

        return new F();
    };
}

来源https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Object/create#Polyfill

 

if (!Function.prototype.bind) {
  Function.prototype.bind = function(oThis) {
    if (typeof this !== 'function') {
      // closest thing possible to the ECMAScript 5
      // internal IsCallable function
      throw new TypeError('Function.prototype.bind - what is trying to be bound is not callable');
    }

    var aArgs   = Array.prototype.slice.call(arguments, 1),
        fToBind = this,
        fNOP    = function() {},
        fBound  = function() {
          // this instanceof fNOP === true时,说明返回的fBound被当做new的构造函数调用
          return fToBind.apply(this instanceof fNOP
                 ? this
                 : oThis,
                 // 获取调用时(fBound)的传参.bind 返回的函数入参往往是这么传递的
                 aArgs.concat(Array.prototype.slice.call(arguments)));
        };

    // 维护原型关系
    if (this.prototype) {
      // Function.prototype doesn't have a prototype property
      fNOP.prototype = this.prototype; 
    }
    // 下行的代码使fBound.prototype是fNOP的实例,因此
    // 返回的fBound若作为new的构造函数,new生成的新对象作为this传入fBound,新对象的__proto__就是fNOP的实例
    fBound.prototype = new fNOP();

    return fBound;
  };
}

来源https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Function/bind