js this

Question 1

What is this in JavaScript?

Answer 1

it’s an implicit parameter

Question 2

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

Answer 2

meaning that 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

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

object character

Question 5

Given the above character object, what is the result of the following code snippet? Why?

character.greet();

Answer 5

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

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

“the object to the left of the dot

Question 8

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

Answer 8

You cant you do not know what the value of this will be.