Understanding assignment of functions to an object in javascript

Question

Hi everybody first time posting here.

So I am trying to understand something, I will post the code here too, but if you want to check out the source, its this " https://www.codecademy.com/en/courses/spencer-sandbox/2/5?curriculum_id=506324b3a7dffd00020bf661 "

Which is an exercise from codeacademy....

So there is bob.setAge = setAge; , why didn't it make it so bob.setAge= newAge; ?? here is the code .

var setAge = function (newAge) {
  this.age = newAge;
};
// now we make bob
var bob = new Object();
bob.age = 30;
bob.setAge = setAge;

// make susan here, and first give her an age of 25
var susan = new Object();
susan.age=25;
susan.setAge = setAge;


// here, update Susan's age to 35 using the method

susan.setAge(35);

setAge is a function ... later you can call it bob.setAge(30). — Aᴍɪʀ
– Aᴍɪʀ, Commented Dec 25, 2015 at 18:13
bob.setAge= setAge define the setAge method of the object to be the function setAge, after that the method could be call and a value passed as parameter. — goupil
– goupil, Commented Dec 25, 2015 at 18:15

m0meni · Accepted Answer · 2015-12-25 18:22:21Z

1

I believe this exercise is trying to teach you the fundamentals of object oriented programming in JavaScript without the syntactic sugar.

More simply stated, they are making a person and that person can have a set of attributes that describe them, and a set of actions they can do.

You've created this function here called setAge

var setAge = function (newAge) {
  this.age = newAge;
};

It'll set the age of an this to newAge. But the question here is what is this? The answer is that it depends, which is why you can reuse this function.

So when you "make bob"

// now we make bob
var bob = new Object();
bob.age = 30;
bob.setAge = setAge;

What you're doing is saying that bob has an action he can do called setAge, and this action is equivalent to the function we defined earlier called setAge. Also in this context this is refers to bob.

So when you do something like bob.setAge(20) then bob.age, represented by this.age will be changed from 30 to 20.

Does that make sense?

Also in your link there is this quote

Great! Now we can take advantage of the fact that the method setAge is not limited to a single object bob

Whether it's bob or susan, you can always use the same setAge function you defined above if you assign it to the object.

edited Dec 25, 2015 at 18:22

answered Dec 25, 2015 at 18:17

m0meni

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6 Comments

Munkiuke Over a year ago

Yes i understand now. thanks a lot.... trying to learn java script can be confusing sometimes but the fast answer was really appreciated thanks again <3

m0meni Over a year ago

Yeah no problem. Glad I was able to get an answer in before they closed it. They can be pretty unfriendly to new programmers here :/

Munkiuke Over a year ago

im new here, i don't even know why they closed it :o. like i just made my account 10 minutes ago and then added my question.

m0meni Over a year ago

@Munkiuke the problem was that you wrote trying to understand how this works in javascript which isn't a very descriptive title. I edited it to make it more clear, but it seems like I was too late. Next time just try to have your title be more specific.

Munkiuke Over a year ago

ohhhhhh alright i understand now. thanks, i will try to be clear in the title next time. what does this ( on hold ) mean ?

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