何时使用“原型"一词?在 javascript 中向对象添加新属性? [英] When to use the word "prototype" in adding new properties to an object in javascript?

问题描述

我不明白在 JavaScript 中什么时候使用原型"这个词与使用简单的点"表示法而不使用原型"这个词.有人可以看看这些代码块并帮助我理解您何时想要使用其中一个?

I don't understand in JavaScript when to use the word "prototype" vs. using simple "dot" notation without the word "prototype". Can someone look at these code blocks and help me understand when you'd want to use one over the other?

带有原型":

function employee(name,jobtitle)
{
  this.name=name;
  this.jobtitle=jobtitle;
}

var fred=new employee("Fred Flintstone","Caveman");
employee.prototype.salary=null;
fred.salary=20000;
console.log(fred.salary);

没有原型":

function employee(name,jobtitle,salary)
{
  this.name=name;
  this.jobtitle=jobtitle;
  this.salary=salary;
}

var fred=new employee("Fred Flintstone","Caveman", 20000);
console.log(fred.salary);

推荐答案

JavaScript 对象有一个属性，它是指向另一个对象的指针.这个指针是对象的原型.默认情况下，对象实例共享相同的原型:

JavaScript objects have a property which is a pointer to another object. This pointer is the object's prototype. Object instances by default share the same prototype:

function Employee(name){
  this.name = name;
}

Employee.prototype.company = "IBM";

Employee.prototype.who = function(){
  console.log("My name is", this.name, "I work for", this.company);
}

var bob = new Employee('Bob');
var jim = new Employee('Jim');

// bob and jim are seperate objects, but each is linked to the same 'prototype' object.

jim.who(); // jim doesn't have a property called 'who', so it falls back to it's 'prototype', where who exists
// My name is Jim I work for IBM

bob.who();
// My name is Bob I work for IBM

// Bob leaves IBM for Microsoft
bob.company = "Microsoft"; // bob now has a property called 'company'. The value of which is 'Microsoft', which overrides bob's prototype property of the same name.

bob.who();
// My name is Bob I work for Microsoft

Employee.prototype.company = 'Facebook';

jim.who(); 
// My name is Jim I work for Facebook

bob.who(); // Bob is not affected by the change.
// My name is Bob I work for Microsoft

delete bob.company;

bob.who(); // bob no longer has it's own property 'company', so like jim, it drops down to the prototype object.
// My name is Bob I work for Facebook

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