javascript-this

Question 1

What is this in JavaScript?

Answer 1

this is an implicit parameter of all JavaScript Functions; a keyword this is determined/defined at the call time

Question 2

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

Answer 2

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

Question 3

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

Answer 3

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!”

Because the greet property has a function and this.firstName is basically character.firstName

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 the hello variable this.firstName would be undefined

Question 7

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

Answer 7

you look at the object

Question 8

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

Answer 8

you look at the object to the left of the dot