JavaScript Quiz

Question 1

What is a variable in programming?

Answer 1

A variable is a bucket we can store data in and a way we can tell our program to remember values for us to use later on.

Question 2

What are the two main things variables allow us to do?

Answer 2

Variables allow us to reuse a value and change a value throughout our program.

Question 3

In variable declaration, what is let age = 25 doing?

Answer 3

let is the declaration (creating a space in memory), age is the assignment (putting stuff in the bucket), and 25 is the argument (the actual value being stored).

Question 4

What types of data can you store in variables?

Answer 4

You can store strings (text surrounded by quotes), numbers (integers and floats like 4.16), and booleans (true/false values).

Question 5

What is camelCase naming convention?

Answer 5

camelCase is a naming convention where the first word is lowercase and subsequent words start with uppercase, like numberOfApples or currentTime.

Question 6

What are the three primitive data types?

Answer 6

Numbers (for calculations and counting), Strings (any sequence of characters including letters, spaces, numbers, or symbols), and Boolean values (representing true/false logical ideas).

Question 7

What can you do with the String data type?

Answer 7

Strings can display data that uses text or symbols, add/remove text, and modify characters.

Question 8

What is the purpose of Boolean values in programming?

Answer 8

Booleans represent logical ideas of true/false. We use them to determine validity and to make decisions in our programs.

Question 9

What does the Number data type allow us to do?

Answer 9

Numbers allow us to describe, calculate, and count values in our programs.

Question 10

What are operators in programming?

Answer 10

Operators are different symbols that represent an operation, such as +, -, *, /.

Question 11

What are the three main categories of operators?

Answer 11

Arithmetic operators (for making calculations), comparison operators (for comparing information), and logical operators (for creating logical expressions).

Question 12

What are the three logical operators?

Answer 12

AND, OR, and NOT operators, which are used to create logical expressions using boolean values.

Question 13

What is the purpose of conditional statements?

Answer 13

Conditionals enable us to make decisions and do something if a statement is true. They are either true or false.

Question 14

What is the basic syntax of an if statement?

Answer 14

if (condition is true) { // Do cool stuff } else if (condition is true) { // Do this other stuff } else { // Other stuff }

Question 15

What are comparison operators and what do they return?

Answer 15

Comparison operators (==, ===, !=, !==, >, <, >=, <=) compare values and always return either TRUE or FALSE.

Question 16

What’s the difference between == and ===?

Answer 16

ERROR!

Question 17

How do you use the AND logical operator (&&)?

Answer 17

AND requires both conditions to be true. Example: if (name === “Leon” && status === “Baller”) { // Do something }

Question 18

How do you use the OR logical operator (||)?

Answer 18

OR requires at least one condition to be true. Example: if (day === “Saturday” || day === “Sunday”) { // It’s the weekend }

Question 19

What is an important rule about assignment (=) vs comparison (==, ===)?

Answer 19

Single equal sign (=) will always be reassignment, while 2-3 equal signs (==, ===) will always be comparison.

Question 20

What is a function?

Answer 20

A function is a simple set of instructions or a named sequence of instructions, packaged as a unit, that performs a specific task.

Question 21

Why are functions important in programming?

Answer 21

Functions form the basic “building blocks” of a program, make code reusable, and allow us to put a set of instructions into memory so we can use it over and over again.

Question 22

What are the two parts of using a function?

Answer 22

Function declaration (when we define a function and specify the instructions, inputs, and name) and function call (when we tell the function to run and execute all its instructions).

Question 23

What is the difference between parameters and arguments?

Answer 23

Parameters are the inputs specified when we define a function. Arguments are the actual values we give for each input when we call the function.

Question 24

When does a function actually run?

Answer 24

A function won’t run unless it’s called. You write it once but can reuse it over and over again by passing in different arguments.

Question 25

What does the example `function yell(word) { alert(word) }` demonstrate?

Answer 25

It shows that `yell` is the function name, `word` is the parameter, and when called like `yell("HELLO")`, the argument "HELLO" falls into the parameter.

Question 26

What is control flow?

Answer 26

Control flow is the order in which each program executes its set of instructions. This order is just as important as the instructions themselves.

Question 27

What are the three types of control structures?

Answer 27

Conditionals (do instructions if something is true), Loops (do instructions a certain number of times), and Exceptions (do instruction set A, but if an error occurs, switch to instruction set B).

Question 28

How do control structures allow for flexibility?

Answer 28

Control structures such as conditionals allow for control flow to be altered during the execution of a program.

Question 29

What example is given for exception handling?

Answer 29

Collect shipping and email address; reject a purchase if either is incorrect.

Question 30

What is the purpose of loops?

Answer 30

Loops enable us to repeat an action some number of times. They are structures in programming where instructions are written once but a computer can execute them multiple times.

Question 31

What are the three types of loops covered?

Answer 31

For loops (count controlled), While loops (condition controlled), and For Each loops (collection controlled).

Question 32

When should you use a for loop?

Answer 32

Use a for loop when you know the number of times you'd like to perform a task before you begin. Each execution is called an "iteration."

Question 33

What is the syntax of a for loop?

Answer 33

for (let i = 1; i < 5; i++) { console.log(i) } where the first part is the initial expression (where the loop starts), second is the condition (when it stops), and third is the increment (what happens each time).

Question 34

When should you use a while loop?

Answer 34

Use a while loop when you know when a program should stop, but not the number of times it should repeat. It's a condition-controlled loop.

Question 35

How does a while loop work?

Answer 35

A while loop repeats a set of instructions while the condition is true. Example: let count = 0; while (count < 5) { console.log(count); count++; }

Question 36

When should you use a for each loop?

Answer 36

Use a for each loop when you need to perform a task for every item in a list, or when the order of things must be maintained.

Question 37

What does a for each loop do?

Answer 37

It defines a sequence and tells the computer to repeat the instructions for each item in the sequence.

Question 38

What is a list (array) in programming?

Answer 38

Lists are one very basic data structure. Programmers use lists as a container to store multiple pieces of information that relate to each other in some way.

Question 39

How is data ordered in an array?

Answer 39

Lists order our data in a specific, linear sequence. The position of a value in a list is known as its index.

Question 40

What number do list indices start at?

Answer 40

List indices are numbers starting with 0. For example: cities = ['NY', 'LA', 'SYD', 'LDN'] has indices 0, 1, 2, 3.

Question 41

How do you add items to the end of a list?

Answer 41

Using the .push() method. Example: myList.push('orange') adds 'orange' to the end.

Question 42

How do you remove the last item from a list?

Answer 42

Using the .pop() method. Example: myList.pop() removes the last item.

Question 43

How do you insert or remove items from the middle of a list?

Answer 43

Using the .splice() method. Example: myList.splice(1,1) removes items from the middle of the list.

Question 44

How do you access an element from an array?

Answer 44

Using the index number. Example: newArr[0] returns 'Zebra', newArr[1] returns undefined if nothing is there.

Question 45

Can you overwrite array values?

Answer 45

Yes, you can overwrite entire arrays by assigning an array to a different array. Example: cars = nums where cars = ['Honda', 'Toyota', 'Ford', 'Tesla'] and nums = [1,2,3].

Question 46

What does array iteration allow you to do?

Answer 46

It iterates through an array, passing in the value and index for each element, allowing you to perform operations on each item.

Question 47

What is the syntax for iterating through an array with forEach?

Answer 47

bestColors.forEach((x, i) => console.log(x)) where x is the element/value and i is the index. The arrow function will run each time.

Question 48

How many times will a forEach loop run?

Answer 48

It's going to run 4 times if there are 4 elements in the array. It's a special function built into JS that will run once for each element in your array.

Question 49

What does the .shift() method do?

Answer 49

It removes an item from the front of an array. Example: let removed = bestRappers2020.shift() removes the value in front of the array.

Question 50

What does the .pop() method do?

Answer 50

It removes an item from the end of an array. Example: let removedAgain = bestRappers2020.pop()

Question 51

What does the .unshift() method do?

Answer 51

It adds an item to the beginning of an array. Example: bestRappers2020.unshift('y') adds 'y' to the front.

Question 52

What does the .push() method do?

Answer 52

It adds an item to the end of an array.

Question 53

What does the .map() method do?

Answer 53

It loops through an array but it creates a new array rather than modifying the original.

Question 54

What is an object in JavaScript?

Answer 54

In JS, everything is an object. Objects are a collection of variables and functions that represent the attributes and behavior of something used in a program.

Question 55

What are object properties?

Answer 55

Object properties are variables attached to an object. They might contain a variable to represent hours, minutes, seconds.

Question 56

What are object methods?

Answer 56

Object methods are functions attached to an object. They might contain functions that manipulate those values, such as start() and stop().

Question 57

How do objects store data?

Answer 57

Objects store "keyed" collections of data as key-value pairs.

Question 58

What is an example of an object representing a stopwatch?

Answer 58

A stopwatch object might have properties (attributes) like hours, minutes, seconds, and methods (behaviors) like start() and stop() functions.

Question 59

What is literal notation for objects?

Answer 59

Literal notation uses the format: let stopwatch = {} where properties use dot notation like stopwatch.currentTime = 12 and method calls use stopwatch.tellTime(stopwatch.currentTime).

Question 60

What is dot notation?

Answer 60

Dot notation is used to access object properties and methods. For properties: object.property, for methods: object.method().

Question 61

When functions are tied to objects, what are they called?

Answer 61

When functions are tied to objects, they are called methods.

Question 62

When individual variables are tied to objects, what are they called?

Answer 62

When individual variables are tied to objects, they are called properties.

Question 63

What is the DOM?

Answer 63

The DOM (Document Object Model) is what happens every time you refresh the page. You're "repainting" the picture, re-rendering and re-reading the HTML, JS, and CSS to paint what you see in the browser.

Question 64

What is an event listener?

Answer 64

An event listener (click) is when they hear the click, they tell a certain set of instructions to run. Example: document.getElementById('purple').onclick = partyPurple

Question 65

What does document.querySelector('body') do?

Answer 65

It selects the body element from the document. You can then modify its style properties like document.querySelector('body').style.backgroundColor = 'rgba...'

Question 66

How can you change text color using DOM manipulation?

Answer 66

Using: document.querySelector('body').style.color = 'white'

Question 67

What is a variable in JavaScript?

Answer 67

A variable is an abstract storage location paired with a symbolic name that holds data. It's like a box where we store information.

Question 68

What are the three ways to declare a variable in JavaScript?

Answer 68

let, const, and var. 'let' allows reassignment, 'const' creates constants that cannot be reassigned, and 'var' is the older method (function-scoped).

Question 69

What are the naming rules for JavaScript variables?

Answer 69

Must start with a letter, $, or _; cannot contain spaces; avoid reserved keywords; use meaningful names.