js this

Question 1

What is this in JavaScript?

Answer 1

keyword for the object you are working with; it’s an implicit parameter

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

Question 3

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

Answer 3

call time; by default this will be given the value of the global window object

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

undefined since the func has not been called

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; it has been called

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!

window object

Question 7

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

Answer 7

not actively using the key thus unable to tell

Question 8

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

Answer 8

the object to the left of the dot

window for a general function