javascript

Question 1

What is the purpose of variables?

Answer 1

The purpose of variables is to store data

Question 2

How do you declare a variable?

Answer 2

var

Question 3

How do you initialize (assign a value to) a variable?

Answer 3

=

Question 4

What characters are allowed in variable names?

Answer 4

letters numbers dollarsign and number not at beggining

Question 5

What does it mean to say that variable names are “case sensitive”?

Answer 5

variables with different cases are different variables

Question 6

What is the purpose of a string?

Answer 6

The purpose of a string is to store text data

Question 7

What is the purpose of a number?

Answer 7

The purpose of a number is to store numbers, and perform math.

Question 8

What is the purpose of a boolean?

Answer 8

The purpose of a boolean is to denote if something is true or false

Question 9

What does the = operator mean in JavaScript?

Answer 9

the equals operator assigns a value to a variable

Question 10

How do you update the value of a variable?

Answer 10

You update the value of a variable by using the = sign

Question 11

What is the difference between null and undefined?

Answer 11

null is assigned on purpose, undefined is not assigned on purpose

Question 12

What is string concatenation?

Answer 12

The operation of combining strings into one single string

Question 13

What data type is returned by comparing two values (,===,etc)?

Answer 13

Boolean

Question 14

What does the += “plus equals” operator do?

Answer 14

It adds a value to a variable. It acts as a shorthand for var = var + value

Question 15

What are objects used for?

Answer 15

For storing different but related pieces of data, and functions to perform operation on related data.

Question 16

What are object properties?

Answer 16

Object properties are variables belonging to an object

Question 17

Describe object literal notation.

Answer 17

Object literal notation is a way of defining an object in javascript.

Question 18

How do you remove a property from an object?

Answer 18

the delete operator

Question 19

What are two ways to get or update the value of a propery?

Answer 19

bracket notation and dot notation

Question 20

What are arrays used for?

Answer 20

Arrays are used for storing data in an indexed format

Question 21

Describe array literal notation

Answer 21

Array literal notation is a way to describe arrays in your code

Question 22

How are arrays different from “plain” objects”

Answer 22

Arrays are indexed

Question 23

What number represents the first index of an array?

Answer 23

0

Question 24

What is the length property of an array?

Answer 24

it gives the number of values in the array

Question 25

How do you calculate the last index of an array

Answer 25

you take the length property and subtract it by one.

Question 26

What is a function in JavaScript?

Answer 26

A function is a block of code that can be run, and have values passed in, and out.

Question 27

Describe the parts of a function definition.

Answer 27

The function name, the function code block, the function return, the function parameters.

Question 28

Describe parts of a function call.

Answer 28

the function name, the function arguments.

Question 29

When comparing them side-by-side, what are the differences between a function call and a function definition?

Answer 29

The function definition has a code block and can have a return statement, the function call has parameter values for arguments.

Question 30

What is the difference between a parameter and an argument?

Answer 30

A parameter describes content that will be passed at some point into a function, an argument is a value being passed into a method we are calling.

Question 31

Why are function parameters useful?

Answer 31

They help us pass data into functions so that they can be self contained (scope)

Question 32

What two effects does a return statement have on the behavior of a function?

Answer 32

It returns a value, and stops code execution of the function code block.

Question 33

Why do we log things to the console?

Answer 33

To debug our code

Question 34

What is a method?

Answer 34

a method is a function belonging to an object

Question 35

How is a method different from any other function?

Answer 35

a method is different because it is called from a function using dot notation

Question 36

How do you remove the last element from an array?

Answer 36

array.pop

Question 37

How do you round a number down to the nearest integer?

Answer 37

Math.floor()

Question 38

How do you generate a random number?

Answer 38

Math.random()

Question 39

How do you delete an element from an array?

Answer 39

array.splice()

Question 40

How do you append an element to an array?

Answer 40

array.push()

Question 41

How do you break a string up into an array?

Answer 41

string.split();

Question 42

Do string methods change the original string? How would you check if you weren't sure?

Answer 42

String methods do not change the original string because strings are immutable. You would check using the console.

Question 43

Roughly how many string methods are there according to the MDN Web docs?

Answer 43

3

Question 44

Is the return value of a function or method useful in every situation?

Answer 44

No

Question 45

Roughly how many array methods are there according to the MDN Web docs?

Answer 45

30

Question 46

What three-letter acronym should you always include in your Google search about a JavaScript method or CSS property?

Answer 46

MDN

Question 47

Give 6 examples of comparison operators.

Answer 47

< > <= >= <== >== == === | | &&

Question 48

What data type do comparison expressions evaluate to?

Answer 48

boolean

Question 49

What is the purpose of an if statement?

Answer 49

Do introduce logic into code

Question 50

Is else required in order to use an if statement?

Answer 50

no

Question 51

Describe the syntax (structure) of an if statement.

Answer 51

conditional code block, condition, conditional statement

Question 52

What are the three logical operators?

Answer 52

if else ( else if )

Question 53

How do you compare two different expressions in the same condition?

Answer 53

you chain them together using an or or an and, you can also use parentheses to group together expressions that should be evaluated first.

Question 54

What is the purpose of a loop?

Answer 54

The purpose of a loop is to iterate through data, or perform an action a certain or indefinite number of times based on a conditional.

Question 55

What is the purpose of a condition expression in a loop.

Answer 55

The purpose of the condition expression is to halt the operation of the condition when certain conditions are met, or to skip over the expression entirely.

Question 56

What does "iteration" mean in the context of loops?

Answer 56

iteration means a repitition of the loop.

Question 57

When does the condition express of a while loop get evaluated?

Answer 57

during the beginning of each iteration.

Question 58

When does the initilization expression for a for loop get evaluated?

Answer 58

during the beginning of the first iteration

Question 59

when does the condition expression of a for loop get evaluated?

Answer 59

during each iteration.

Question 60

When does the final expression of a for loop get evaluated?

Answer 60

the beginning of each iteration before the conditional.

Question 61

Besides a return statement, which exits its entire function block, which keyword exits a loop before its condition expression evaluated to false?

Answer 61

break

Question 62

What does the ++ increment operator do?

Answer 62

adds 1 to a variable

Question 63

How do you iterate through the keys of an object?

Answer 63

Using a for each loop

Question 64

What event is fired when a user places their cursor in a form control?

Answer 64

hover

Question 65

What event is fired when a user's cursor leaves a form control?

Answer 65

blur

Question 66

What event is fired as a user changes the value of a form control?

Answer 66

input

Question 67

What event is fired when a user clicks the "submit" button within a ?

Answer 67

submit

Question 68

What does the event.preventDefault() method do?

Answer 68

prevents a form from performing its default action when used.

Question 69

What property of a form element object contains all of the form's controls.

Answer 69

elements

Question 70

What property of form a control object gets and sets its value?

Answer 70

name.value

Question 71

What is one risk of writing a lot of code without checking to see if it works so far?

Answer 71

bugs, long debug times

Question 72

What is an advantage of having your console open when writing a JavaScript program?

Answer 72

you can see bugs right away.

Question 73

What is JSON?

Answer 73

JSON is a way of storing JavaScript objects in strings

Question 74

What are serialization and deserialization?

Answer 74

They are the process of taking data and organizing it in a way that can be better understood

Question 75

Why are serialization and deserialization useful?

Answer 75

They allow us to transmit and receive data in formats that are usable.

Question 76

How do you serialize a data structure into a JSON string using JavaScript?

Answer 76

JSON.stringify()

Question 77

How do you deserialize a JSON string into a data structure using JavaScript?

Answer 77

JSON.parse()

Question 78

What does the new operator do?

Answer 78

The new operator creates a new instance of a function and runs it.

Question 79

What property of JavaScript functions can store shared behavior for instances created with new?

Answer 79

prototype

Question 80

What does the instanceof operator do?

Answer 80

Checks if the prototype is an instance of a function

Question 81

What kind of inheritance does the JavaScript programming language use?

Answer 81

prototypal inheretence

Question 82

What is a prototype in JavaScript?

Answer 82

A prototype is an object that stores functions.

Question 83

How is it possible to call methods on strings, arrays, and numbers even though those methods don't actually exist on objects, arrays, and numbers?

Answer 83

inheretence

Question 84

If an object does not have it's own property or method by a given key, where does JavaScript look for it?

Answer 84

it's protoype chain

Question 85

What is this in JavaScript?

Answer 85

this refers to the current instance of the object

Question 86

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

Answer 86

it is included with every function

Question 87

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

Answer 87

during run time

Question 88

What is a method?

Answer 88

A method is a function belonging to an object

Question 89

How can you tell the difference between a method definition and a method call?

Answer 89

A method definition has no parentheses, and has a code block

Question 90

Describe method definition syntax (structure).

Answer 90

function hello(name) { }

Question 91

Describe method call syntax (structure).

Answer 91

hello('humberto')

Question 92

How is a method different from any other function?

Answer 92

A method is different because it belongs to an object

Question 93

What are the four "principles" of Object-Oriented Programming?

Answer 93

Abstraction Inheretence Polymorphism Encapsulation

Question 94

What is "abstraction"?

Answer 94

Taking something complex and making it easy to use

Question 95

What does API stand for?

Answer 95

Application programming interface

Question 96

What is the purpose of an API?

Answer 96

To make it easy for others to use data in your application in their programs.