Why Do I Have To Use "this" To Access In Inner Property Of A Function

What is the difference between function person(first_name, last_name) { this.first = first_name this.last = last_name } and this: function person(first_name, last_name) {

Solution 1:

The this keyword within a function is called the invocation context.

1) If you define your function as a member of an object (a method):

myObject.someMethod = function() { this.x = 2; };

then the invocation context, this, is the object to which the method is being added, myObject. So after calling myObject.someMethod(); above, myObject.x is then 2. The member x is undefined until you call the method, unless you defined it before.

2) If you use your function as a constructor with the new keyword, then this refers to the new object that is being created:

function MyX() { this.x = 3; };
var myX = new MyX();

You'll then have property myX.x set to 3.

Note that I called my constructor MyX(), not myX(). You should call yours Person(), not person(). It's just a convention, but it is useful to indicate that a function is meant to be used as a constructor.

3) Finally, if you use this within a function that you call as neither a method nor a constructor, then this refers to the global object (document or, equivalently, window). Note however that if you are using javascript in strict mode (which you should do), this is undefined in such a situation, which means that you basically cannot use this in a function that is not a method or a constructor.

---

Your specific question refers to case 2), the constructor. this.x = 3 in the constructor just sets property x of the newly created object. After some object myX is created, you can then access and modify x externally as any other object property using myX.x.

Solution 2:

when you write constructor function ( using new) - you add properties using this.XXX

then you do :

var p = new Person('s','d');

and then you have access to p.first etc.

in the second example : youre not creating any properties..

youre only creating private variables.

so you cant access them...

Solution 3:

By using this.something you're saying that THIS is an object and something is his property.

By using var, you're saying that it's just a variable and not a property.

More information about variable vs property: http://javascriptweblog.wordpress.com/2010/08/09/variables-vs-properties-in-javascript/

Solution 4:

Because of function scope.

A variable lifetime is between the curly braces of the function. The this keyword allows to access the function properties outside of it.

Definitely take a look at this link: https://developer.mozilla.org/en/JavaScript/Reference/Functions_and_function_scope

Solution 5:

'var' keyword make a variable scoped. In the last example var first and var last create variable accessible only in the scope of the function. You can see this as a local variable in a constructor.