The keyword of this

JavaScript
1 
function Hero() {
this.occupation = 'Ninja';
}

don’t understand the meaning of this line ,this.occupation = ‘Ninja’; why it use this keyword. thank you.

2

The function in your example is set up to act as a constructor for Hero objects. If it is called with the ‘new’ keyword, it will return an object.


// define a constructor for Hero objects.
// notice the capital H for the function name.
function Hero() {}

// use the constructor to create a Hero instance
var myHero = new Hero();

// myHero now points to an instance of the Hero 'class'
alert(myHero instanceof Hero); // true

Within the constructor, ‘this’ refers to the object that will be returned. It can be used to add properties to the object.


function Hero() {
  this.occupation = 'Ninja';
}

var myHero = new Hero();
alert(myHero instanceof Hero); // still true

// use the property set in the constructor
alert(myHero.occupation); // Ninja

The constructor can accept arguments to be used to initialise the object returned


function Hero(job) {
  this.occupation = job;
}

var myHero = new Hero("Ninja");
var yourHero = new Hero("Estate Agent");

alert(myHero.occupation); // Ninja
alert(yourHero.occupation); // Estate Agent