阴影属性如何在 Object 具有相同名称属性的面向编程中工作

Question

const myDate = new Date(1995, 11, 17);

console.log(myDate.getYear()); // 95

myDate.getYear = function() {
  console.log('something else!')
};

myDate.getYear(); // 'something else!'

In this uploaded code the expected output is "something else" but I cannot understand how it will create shadowing when we define a object with the same name in Object prototype and how constructor function work on it

Answer 1

Javascript inheritance works by defineing new methods on an object instance of a prototype class. Eg. if you are extending a class Base you make a new function and set its protype to an instance of Base and then add whatever method you would want extra on that instance.

An instance is a empty object with a pointer to the prototype. The logic in accessing a property is to check its own object first, then fllow the prototype chain and eventually return undefined when a property isn't in any. Eg. if you write this.getYear before and after setting it you will get two different results because the accessor will start finding the property on the instance and then end its search.

V8 and modern JS engines has oprtimizations to not have to go down this rabbit hole, but it should still work the same as if it still was a linked list of objects.

And of course. Any property can be a method and you cannot have a method and a property have the same name since they share namespace. Eg. you could do this myDate.getYear = 2022; such that myDate.getYear would return 2022 , but myDate.getYear() would end with a application error since the property does not hold a function object that can be applied.