Javascript-this-Q&A

Question 1

What is this in JavaScript?

Answer 1

“This” is the reference of the lexical scope of the function at call time

Question 2

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

Answer 2

We dont specifically define it but it is still available

Question 3

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

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

the value of the firstName property of the character object

Question 5

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

Answer 5

the console.log message (Its a me mario)

Question 6

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

Answer 6

undefended (its a me ‘undefined’)

Question 7

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

Answer 7

There is no way to know when it is not defined at definition time

Question 8

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

Answer 8

look at the lexical scope of where it is being called