Reference Types

Question 0

What are reference types?

Answer 0

Structures used to group data and functionality together

Question 1

What is a reference value an instance of?

Answer 1

A specific reference type

Question 2

Are there classes in JavaScript?

Answer 2

No. JacaScript does not support classss.

Question 3

What is another name for reference types?

Answer 3

Object definitions

Question 4

What is a constructor?

Answer 4

A simple function who’s purpose is to create an object.

Question 5

What are objects an instance of?

Answer 5

A particular reference type.

Question 6

What are two ways to create an instance of the Object type?

Answer 6

1. The new operator:
var person = new Object();

2. Object literal notation:
var person = {};

Question 7

What is an expression context in ECMAScript?

Answer 7

A context in which a value (expression) is expected

Question 8

How can you define an object so the Object constructor is never called?

Answer 8

An object defined via object literal notation never calls the Object constructor.

Question 9

What type of data can an array hold?

Answer 9

Arrays can hold any type of data in each slot.

Question 10

How are arrays sized?

Answer 10

Arrays are dynamically sized, automatically growing to accommodate any data that is added to them.

Question 11

What two ways can arrays be created?

Answer 11

Using the array constructor:
var colors = new Array();

Using array literal notation:
var colors = [];

Question 12

How can you initialize an Array if you know the amount of items that will be in the array?

Answer 12

var colors = new Array(20);

This will create an array with an initial length of 20.

Question 13

When an array is created using array literal notation is the Array constructor called?

Answer 13

No.

Question 14

What happens in this example:
var colors = ["red", "blue"];
colors[2] = "green";

Answer 14

The array length is automatically expanded to be that index plus 1

Question 15

Where is the number of items of an array stored?

Answer 15

In the length property, which always returns 0 or more.

Question 16

What happens in the following example?
var colors = ["red", "blue", "green"];
colors.length = 1;

Answer 16

The last item is removed from the array. The length property is not read only.

Question 17

How can you add an element to the end of an array using the length property?

Answer 17

colors[colors.length] = “black”

Question 18

What is the maximum amount of items an array can contain?

Answer 18

4,294,967,295 items.

If you try to add more an exception occurs.

Question 19

What are two ways you can detect if a given object is an array?

Answer 19

The instanceof operator and the Array.isArray() method.

Use isArray if there are multiple global contexts

Question 20

When should you use Array.isArray();?

Answer 20

When detecting if an object is an array and dealing with multiple global scopes.

Question 21

How can you get a comma-separated string of all of the items within a given array?

Answer 21

colors. toString();

colors. valueOf();