JavaScript

Question 1

What is the purpose of variables?

Answer 1

To store or remember information.

Question 2

How do you declare a variable?

Answer 2

• var
• let
• const

Question 3

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

Answer 3

Using one equal sign.

Question 4

What characters are allowed in variable names?

Answer 4

• Variable names must start with a letter, underscore, or dollar sign.
• Variable names cannot contain spaces.
• Variable names can only contain letters, numbers, underscores, and dollar signs.
• Variable names are case-sensitive.

Question 5

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

Answer 5

Variable names have to be specific. (firstname & firstName are two different variables).

Question 6

What is the purpose of a string?

Answer 6

Used to represent and manipulate a series of characters.

Question 7

What is the purpose if a number?

Answer 7

Used to represent and manipulate numbers.

Question 8

What is the purpose of a boolean?

Answer 8

Used when determining which part of a script should run. (True or false).

Question 9

What does the = operator mean in JavaScript?

Answer 9

Assigns a value to a variable.

Question 10

How do you update the value of a variable?

Answer 10

By using the name of the variable and assigning it a new value.

Question 11

What is the difference between null and undefined?

Answer 11

• Null is a type of object that is intentionally given no value.
• Undefined is when a variable is defined, but never given a value.

Question 12

What data type is returned by an arithmetic operation?

Answer 12

Number.

Question 13

What is a string concatenation?

Answer 13

Joining strings together to create one new string.

Question 14

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

Answer 14

To add numbers and concatenate strings.

Question 15

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

Answer 15

Boolean.

Question 16

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

Answer 16

It adds the value of the right operand to a variable and assigns the result to the variable.

Question 17

What are objects used for?

Answer 17

To group together a set of variables and functions to create a model of something you would recognize from the real world.

Question 18

What are object properties?

Answer 18

• Variables with values.

* Allow us to store information in an object literal.

Question 19

Describe literal notation.

Answer 19

• Assigning an object literal to a variable.

* Within the object, there are properties (variables) and methods (functions).

Question 20

How do you remove a property from an object?

Answer 20

• By using the delete keyword followed by the object name and property name
• By using the delete operator.

Question 21

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

Answer 21

• object.property-name = value - Dot Notation

* object[‘property-name’] = value - Bracket Notation

Question 22

Why do we log things to the console?

Answer 22

To debug and see if the output is what you want it to be.

Question 23

What is a method?

Answer 23

A function which is a property of an object.

Question 24

How is a method different from any other function?

Answer 24

A method is associated/attached with an object.

Question 25

How do you remove the last element from an array?

Answer 25

Using the Array.prototype.pop() method.

Question 26

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

Answer 26

Using the Math.floor() method.

Question 27

How do you generate a random number?

Answer 27

Using the Math.random() method.

Question 28

How do you delete an element from an array?

Answer 28

Using the Array.prototype.splice() method.

Question 29

How do you append an element to an array?

Answer 29

Using the Array.prototype.push() method.

Question 30

How do you break a string up into an array?

Answer 30

Using the String.prototype.split() method.

Question 31

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

Answer 31

They do not, they are immutable, and only reassign the variable. You would check by looking at the documentation or console log.

Question 32

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

Answer 32

About 30 string methods.

Question 33

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

Answer 33

No, you don't always need to use the return value.

Question 34

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

Answer 34

About 30 array methods.

Question 35

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

Answer 35

MDN.

Question 36

What is the purpose of a loop?

Answer 36

• To run a certain block of code as fast as possible until something tells it to stop.

Question 37

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

Answer 37

To tell the loop when to start and stop.

Question 38

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

Answer 38

Iteration means how many times the code in the loop runs.

Question 39

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

Answer 39

Before each pass through the loop.

Question 40

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

Answer 40

Once, before the loop begins.

Question 41

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

Answer 41

Before each loop iteration.

Question 42

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

Answer 42

At the end of each loop iteration.

Question 43

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

Answer 43

Break.

Question 44

What does the ++ increment operator do?

Answer 44

It increments a number up by one.

Question 45

How do you iterate through the keys of an object?

Answer 45

By using a for...in loop.

Question 46

Give 6 examples of comparison operators.

Answer 46

* > - (Greater Than) * < - (Less Than) * === - (Strictly Equal To) * == - (Equal To) * != - (Is Not Equal To) * !== - (Strictly Not Equal To)

Question 47

What data type do comparison expressions evaluate to?

Answer 47

Boolean.

Question 48

What is the purpose of an if statement?

Answer 48

• To make decisions in our code.

Question 49

Is else required in order to use an if statement?

Answer 49

No.

Question 50

Describe the syntax (structure) of an if statement.

Answer 50

* if Keyword * condition * code block

Question 51

What are the three logical operators?

Answer 51

* && - (Logical And) * || - (Logical Or) * ! - (Logical Not)

Question 52

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

Answer 52

By using a logical operator.

Question 53

What is a function in JavaScript?

Answer 53

A series of steps that are performed when they are called and passed a value.

Question 54

Describe the parts of a function definition.

Answer 54

* The Function Keyword. * The name of the function (optional). * Parameters surrounded by parentheses. * The function's code block {}. * Return Statement (optional).

Question 55

Describe the parts of a function call.

Answer 55

* Function Name. | * (Arguments).

Question 56

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

Answer 56

* The function definition holds all the code. | * The function call runs the code.

Question 57

What is the difference between a parameter and an argument?

Answer 57

* A parameter is a placeholder. | * An argument is what is passed through the function when we call a function.

Question 58

Why are function parameters useful?

Answer 58

To know what value(s) to pass through as the argument when calling a function.

Question 59

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

Answer 59

* It causes the function to produce a value we can use in our program. * It will prevent any more code in the function's code block from being run.

Question 60

What are arrays used for?

Answer 60

To store a list of values.

Question 61

Describe array literal notation.

Answer 61

var array-name = []

Question 62

How are arrays different from "plain" objects?

Answer 62

* They are numerically indexed. | * They are designed to be used as a list.

Question 63

What number represents the first index of an array?

Answer 63

0.

Question 64

What is the length property of an array?

Answer 64

• The number of values in an array.

Question 65

How do you calculate the last index of an array?

Answer 65

array.length - 1.