What is the difference between a method and a function? / This might be a dumb question, but what is the difference between methods and functions, if there are any?

this is not a dumb question! It's really important.

A method is a function that belongs to a class. It is invoked by specifying an object of that class, a dot, and the name of the method, and then its arguments.


    // the following are functions, not methods
    let d = getTestDate();
    updatePage();
    // The following are methods
    x = 'hello';
    x.indexOf('o'); // returns 4
    x.charAt(4);    // returns 'o'
    x.bold();       // returns "<b>hello</b>"

If you've been coding in Java, it's easy to forget, because Java (as we know it) doesn't have functions; it only has methods.

However, newer versions of Java have added functions back in, partly because of the need for callback functions, which is exactly why we are learning them.

why would we use "this" instead of just repeating the value name? efficiency?

We use this because that's how OOP works: we define methods to operate on objects of different kinds. The code for deposit on a bank account can't know what bank balance to increment. It operates on this.

2 x Why does this code work if the value of ""this"" changes in anonymous functions?

var hat = [10, 20, 30, 40]; // total of 100
hat.map(function (amt) { ron.deposit(amt) });"

Because the function doesn't refer to this, so the fact that this has the wrong value doesn't cause trouble.

Could you go over why this failed, I don't quite understand why?

class Account {
    ...
    depositAll (hat) {
        console.log(this.balance);  // works
        hat.map(function (amt) { this.deposit(amt) });
    }
    ...
}

The function above refers to this, which has the wrong value, and so disaster ensues.

But if we used an arrow function instead, all would be well.

Can you further explain the logic of invoking a normal function changes the value of this?
Can you explain more on why the the keyword ""this"" has the wrong value?
could you explain why invoking a normal function changes the value of this?

Those are the rules for the invocation of ordinary functions. When JS was created, Brendan Eich knew he wanted OOP and functions, and that functions would refer to this and so this had to be bound when invoking a function.

So if we invoke a function inside a method, we have to take that into account.

Can we talk more about ""Methods as Arguments""?

Sure. Suppose we are doing two things:

using functions as arguments, to things like .click and .forEach
using OOP, so we have methods to do things

If we are doing both, we have to think for a minute before passing a method as an argument to a function: namely, what will the object be?

Sometimes, we need to use the .bind method to specify the object.