在javascript中使用原型

Question

I am learning prototype in JavaScript and this is the code I am trying -

<script>
function employee(name, age, sex) {
    this.name = name;
    this.age = age;
    this.sex = sex;
}

var trialcoder = new employee('trialcoder', 26, 'M');
//employee.prototype.salary = null;
trialcoder.salary = 19000;

document.write("salary is "+ trialcoder.salary);
</script>

My thoughts - To add another property we need to use prototype like - employee.prototype.salary = null; so on un commenting this line, I was expecting an error but it was not..let me know where I am wrong in the prototype concept.

Code Source - http://www.w3schools.com/jsref/jsref_prototype_math.asp

Answer 1

Your code is correct, because when you called

var trialcoder = new employee('trialcoder', 26, 'M');

You got an object instance of employee and just like any other object you can add properties to your trialcoder object like

trialcoder.salary = 19000;

In this case, the salary property is only available to your trialcoder object and if you make another instance of employee like var another = new employee() you have no salary property in another object, but, if you do something like

function employee(name, age, sex) { //... }
employee.prototype.salary = 19000;

and then make instances like

var anEmp = new employee();
console.log(anEmp.salary); // 19000

Make another instance

var newEmp = new employee();
console.log(newEmp.salary); // 19000

if you want, you can

newEmp.salary = 10000;
console.log(anEmp.salary); // 10000

Which means, when you add a property in the prototype of a constructor (employee) then every object instance can share the same property and after making an instance from the constructor, you can change the property of an instance but this won't effect other instances. Hope it's clear enough now.

Answer 2

您的代码是正确的，并且不会收到错误，因为使用原型设置类雇员的设置属性薪金，并在创建类的对象ur后为该特定对象设置属性，如果创建另一个对象，则也可以设置其属性薪水如果使用原型设置属性，则该类的所有对象都将共享该（工资）属性。