'this'when creating javascript object

Question

I'm studying javaScript object. I learned to create objects in this format, but I don't understand 'this' keyword very well.

var Person = function(name, age){
    this.name = name;
    this.age = age;
}

I think the 'this' written here is global variable. However, even though there are no names and ages defined as global variables, this constructor works well.like this.

var Person = function(name, age){
    this.name = name;
    this.age = age;
}

var john = new Person('john',19);
console.log(john.name); //result : 'john'
console.log(john.age);  //result : 19

I don't know why it works like this. When I write code like this,

var Person = function(){
    console.log(this);  //result : window
    console.log(this.name);  //result : '' // <--I don't know why empty string is printed on this part, too.
    console.log(this.job);  //result : undefined
}
Person();

I thought 'this' is pointing to the global variable. But I think there's something I'm wrong about. I would appreciate it if you could tell me why can use 'this' keyword when make an object like this.

P.S)What I know is that this : When 'this' is written in the method in the object means the object in which 'this' is written, and that when it is used in other parts, it means global variable.

'this'when creating javascript object

0 Answers0