Question

Hello I’m a newcomerin JavaScript language.
I started to see some examples of JavaScript code.

and i cant understand the following code segment:

function Employee(name,salary)
 {
  this.name=name;
  this.salary=salary;

  this.paycheck=function()
  {
   var monthly=this.salary/12;
   document.write(this.name+ ": " +monthly);
  };
} 
var emp= new Employee("Fred",10000);
emp.paycheck();

My question: what is the meaning of word this near the property inside class (i.e. ,this.name=name; this.salary=salary; )?

Thank you in advance!

Answer 1

The use of this could be explained as meaning “properties that apply to this instance”. Since Employee is a constructor function (you create instances of it using the new operator), every instance has its own values for those properties:

var me = new Employee("James", 2000000); //Instance of Employee
console.log(me.name); //Prints James

var you = new Employee("Michael", 2000000); //Another instance
console.log(you.name); //Prints Michael

Note that this also means every instance of Employee has its own copy of the paycheck method. This is not particularly efficient, as a separate copy of the function has to be stored in memory for every instance of the object. You could instead declare the method on the prototype of the Employee object, which would mean the method would be shared between all instances.