javascript-this

Question 1

What is this in JavaScript?

Answer 1

A better question will be when is this, this is an implicit parameter, whose value is determined by when the function is called and not defined

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 not included as a parameter 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 object ‘character’.

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!

.greet() is a method on 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!

the ‘this.firstName’ is bound to the values in ‘character’ which the ‘hello’ variable does not have.

Question 7

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

Answer 7

The code block it is nested in. If it’s within an object, ‘this’ refers to the object. If it’s within a function declared in the global scope, it refers to the window

Question 8

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

Answer 8

This is determined when the function or method is called