Javascript-this

Question 1

What is this in JavaScript?

Answer 1

‘this’ refers to any object related at the moment the function is called.

Question 2

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

Answer 2

It is available despite not being declared within function

Question 3

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

Answer 3

at call 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 Character object

Question 5

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

Answer 5

It’s a-me, Mario!
this is referring to the character object, so you’re calling the firstName property of the character object.

Question 6

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

Answer 6

It’s a-me, undefined!
At the moment of call there is no object.

Question 7

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

Answer 7

look at what object the function with this is contained in.

Question 8

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

Answer 8

look to left of the function.