JavaScript

Question 1

What is the purpose of variables?

Answer 1

To store bits of data

Question 2

How do you declare a variable?

Answer 2

With a variable keyword (var, let, const) followed by the variable name

Question 3

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

Answer 3

With an assignment operator (=)

Question 4

What characters are allowed in variable names?

Answer 4

letters, digits, underscores and dollar signs (CANNOT START WITH NUMBER)

Question 5

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

Answer 5

upper and lowercase matter

Question 6

What is the purpose of a string?

Answer 6

To store text data

Question 7

What is the purpose of a number?

Answer 7

To store number data

Question 8

What is the purpose of a boolean?

Answer 8

To identify true or false

Question 9

What does the = operator mean in JavaScript?

Answer 9

Assignment operator

Question 10

How do you update the value of a variable?

Answer 10

By calling again with the assignment operator followed by the new value

Question 11

What is the difference between null and undefined?

Answer 11

Null usually a placeholder

Undefined points at valueless variables

Question 12

Why is it a good habit to include “labels” when you log values to the browser console?

Answer 12

Describes the variable or value being logged

Question 13

Give five examples of JavaScript primitives.

Answer 13

String
Boolean
Object
Undefined
Null

Question 14

What data type is returned by an arithmetic operation?

Answer 14

Number

Question 15

What is string concatenation?

Answer 15

When two or more lines of strings are combined using the addition operator

Question 16

What purpose(s) does the + plus operator serve in JavaScript?

Answer 16

Adds one value to another

Question 17

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

Answer 17

Boolean

Question 18

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

Answer 18

Adds the value of the right operand to a variable and assigns the result to the variable

Question 19

What are objects used for?

Answer 19

To represent real world objects

Question 20

What are object properties?

Answer 20

Information about the object

Question 21

How do you remove a property from an object?

Answer 21

With the delete operator

Question 22

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

Answer 22

Dot and Bracket notation

Question 23

What are arrays used for?

Answer 23

To store list data

Question 24

Describe array literal notation.

Answer 24

var arrayName = [’’]

Question 25

How are arrays different from "plain" objects?

Answer 25

Arrays have indexes objects dont

Question 26

What number represents the first index of an array?

Answer 26

array[0]

Question 27

What is the length property of an array?

Answer 27

Represents the number of properties in that array

Question 28

How do you calculate the last index of an array?

Answer 28

array[array.length -1]

Question 29

What is a function in JavaScript?

Answer 29

A pack of code to reuse

Question 30

Describe the parts of a function definition.

Answer 30

function funcName(parameter,/.../,parameter) { code .../ return; code .../ }

Question 31

Describe the parts of a function call.

Answer 31

funcName(parameter,/.../,parameter);

Question 32

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

Answer 32

No code block

Question 33

What is the difference between a parameter and an argument?

Answer 33

Arguments are real values being passed to the function, while parameters are just placeholder names

Question 34

Why are function parameters useful?

Answer 34

Specify what the argument should be

Question 35

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

Answer 35

Returns the function when being called Stops the code from running

Question 36

Why do we log things to the console?

Answer 36

To check our work

Question 37

What is a method?

Answer 37

Function of an object

Question 38

How is a method different from any other function?

Answer 38

It's a property of an object

Question 39

How do you remove the last element from an array?

Answer 39

With the array.pop(); method

Question 40

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

Answer 40

With the Math.floor() method

Question 41

How do you generate a random number?

Answer 41

With the Math.random(); method

Question 42

How do you delete an element from an array?

Answer 42

With the array.splice(index,amount);

Question 43

How do you append an element to an array?

Answer 43

With the push(); method

Question 44

How do you break a string up into an array?

Answer 44

With the split() method

Question 45

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

Answer 45

They dont

Question 46

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

Answer 46

Around 50

Question 47

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

Answer 47

No, you may use it later on

Question 48

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

Answer 48

40-50

Question 49

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

Answer 49

mdn

Question 50

What data type do comparison expressions evaluate to?

Answer 50

Booleans

Question 51

What is the purpose of an if statement?

Answer 51

To execute a block of code when the condition is met or not

Question 52

Is else required in order to use an if statement?

Answer 52

else

Question 53

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

Answer 53

&& ||

Question 54

What is the purpose of a loop?

Answer 54

Easy way to do something repeatedly

Question 55

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

Answer 55

To let it know when to start and stop

Question 56

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

Answer 56

To repeat

Question 57

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

Answer 57

At the beginning

Question 58

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

Answer 58

At the very start

Question 59

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

Answer 59

After every initialization and after every loop

Question 60

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

Answer 60

After the iteration

Question 61

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

Answer 61

The Break; Key

Question 62

What does the ++ increment operator do?

Answer 62

Increment the value by one

Question 63

How do you iterate through the keys of an object?

Answer 63

With a for in loops for ( var prop in obj ) { code }

Question 64

Why do we log things to the console?

Answer 64

To keep track that everything is working.

Question 65

What is a "model"?

Answer 65

A "model" is a memory saved model created with nodes representing an HTML element (DOM tree)

Question 66

Which "document" is being referred to in the phrase Document Object Model?

Answer 66

The HTML document currently being worked on

Question 67

What is the word "object" referring to in the phrase Document Object Model?

Answer 67

DOM Tree nodes

Question 68

Give two examples of document methods that retrieve a single element from the DOM.

Answer 68

getElementById() querySelector()

Question 69

Give one example of a document method that retrieves multiple elements from the DOM at once.

Answer 69

querySelectorAll()

Question 70

Why might you assign the return value of DOM query to a variable?

Answer 70

To refer back to it

Question 71

What console method allows you to inspect the properties of a DOM element object?

Answer 71

console.dir()

Question 72

Why would