javascript-this

Question 1

What is this in JavaScript?

Answer 1

It is an implicit parameter of all JavaScript functions.

Question 2

What does it mean to say that this is an “implicit parameter”?

Answer 2

it is available in a function’s code block even though it was never included in the function’s parameter list or declared with var

Question 3

When is the value of this determined in a function; call time or definition time?

Answer 3

the value of this is determined when the function is called

Question 4

What does this refer to in the following code snippet?
var character = {
  firstName: 'Mario',
  greet: function () {
    var message = 'It\'s-a-me, ' + this.firstName + '!';
    console.log(message);
  }
};

Answer 4

there’s no this yet; it’s not being called.

Question 5

Given the above character object, what is the result of the following code snippet? Why?
character.greet();
I

Answer 5

t’s-a-me, Mario!’

Because the var ‘character’ is being passed as the obj.

Question 6

Given the above character object, what is the result of the following code snippet? Why?
var hello = character.greet;
hello();

Answer 6

Undefined; because of window is default value for this.

Question 7

How can you tell what the value of this will be for a particular function or method definition?

Answer 7

if you cannot see the function being called, then you do not know what the value of this will be.

Question 8

How can you tell what the value of this is for a particular function or method call?

Answer 8

Look for an object to the left of the dot.