Javascript

Question 1

What are arrays used for?

Answer 1

Storing lists, especially lists of ordered or related data.

Question 2

Describe array literal notation.

Answer 2

Comma-delineated items between square brackets.

[ item1, item2 . . . ]

Question 3

How are arrays different from “plain” objects?

Answer 3

The keys in arrays are numbers instead of strings; Arrays are numerically indexed.

Question 4

What number represents the first index of an array?

Answer 4

0

Question 5

What is the length property of an array?

Answer 5

The number of items in the array.

Question 6

How do you calculate the last index of an array?

Answer 6

arrayLength - 1

Question 7

What are objects used for?

Answer 7

They group together related information (ie. variables and functions)

In OOP (object oriented programming) objects are used to model areal-world objects.

Question 8

What are object properties?

Answer 8

Key-value pairs consisting of a property and its value.

Question 9

Describe object literal notation.

Answer 9

Comma-delineated key-value pairs between curly braces.

{ prop1: val1, prop2: val2, . . . }

Question 10

How do you remove a property from an object?

Answer 10

The delete operator.

Question 11

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

Answer 11

Dot notation (using member operator) and bracket notation

Question 12

What data type is returned by an arithmetic operation?

Answer 12

number

Question 13

What is string concatenation?

Answer 13

Joining strings together

Question 14

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

Answer 14

Adding numbers and concatenating 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 is shorthand for performing addition or concatenation and then assigning the result to the variable on the left.

Question 17

What is the purpose of variables?

Answer 17

Temporarily store pieces of data while a program is running.

Question 18

How do you declare a variable?

Answer 18

Using the keyword const, let, or var followed by the variable name

Question 19

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

Answer 19

using the assignment operator (=)
var varName = aValue;

Question 20

What characters are allowed in variable names?

Answer 20

Letters, numbers, $, and _ (underscore). Variables names cannot start with a number.

Question 21

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

Answer 21

Lower and upper case letters are considered different characters.

Question 22

What is the purpose of a string?

Answer 22

Store and represent text date/characters

Question 23

What is the purpose of a number?

Answer 23

Represent/store numeric data so you can do math/arithmetic.

Question 24

What is the purpose of a boolean?

Answer 24

To represent/store binary data which lets you do logic

Question 25

What is the difference between null and undefined?

Answer 25

Undefined means ‘no value given yet’; null explicitly means ‘nothing’ or ‘intentional absence’

Question 26

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

Answer 26

Helps with debugging since a label can indicate where and what variable a value comes from.

Question 27

Give five examples of JavaScript primitives

Answer 27

string, number, boolean, undefined, null, ...symbol is also a type

Question 28

What is a function in JavaScript?

Answer 28

A named, reusable block of code that performs a task. Functions can accept inputs and return outputs

Question 29

Describe the parts of a function definition.

Answer 29

1. The function keyword 2. optional function name 3. list of 0 or more parameters, 4. code block surrounded by curly braces, 5. optional return statement inside the code block

Question 30

Describe the parts of a function call.

Answer 30

1. Function name | 2. pair of parentheses, containing arguments

Question 31

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

Answer 31

A function definition contains the function keyword and a code block, function call does not have these

Question 32

What is the difference between a parameter and an argument?

Answer 32

Parameters appear in the function definition. Arguments are the actual input values a function is called with.

Question 33

Why are function parameters useful?

Answer 33

Parameters let you pass inputs into a function for it to use

Question 34

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

Answer 34

1. causes the function to stop running/exits the function.A return statement also 2. causes the function to produce a value/output that can then be used by the rest of your program

Question 35

Why do we log things to the console?

Answer 35

To know what your data looks like; Logging to console lets you check the value of a variable at a specific place/time in the running of the code

Question 36

What is a method?

Answer 36

A method is a function which is a property of an object.

Question 37

How is a method different from any other function?

Answer 37

A method is part of/associated with an object. A function is not.

Question 38

How do you remove the last element from an array?

Answer 38

array.pop() method

Question 39

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

Answer 39

Math.floor()

Question 40

How do you generate a random number?

Answer 40

Math.random() method

Question 41

How do you delete an element from an array?

Answer 41

Array.splice() method

Question 42

How do you append an element to an array?

Answer 42

Array.push()

Question 43

How do you break a string up into an array?

Answer 43

String.split()

Question 44

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

Answer 44

No, because strings are immutable. Log to console or check MDN to check yourself.

Question 45

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

Answer 45

No. Just because a function returns a value doesn't mean you have to use it.

Question 46

What is the purpose of a loop?

Answer 46

Repeating a block of code a set number of times.

Question 47

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

Answer 47

Checks if it’s time for the loop to stop

Question 48

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

Answer 48

A single run of the code in the loop’s code block

Question 49

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

Answer 49

Before each iteration of the while-loop.

Question 50

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

Answer 50

Once before the loop begins any iterations

Question 51

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

Answer 51

Before the first iteration and then before each subsequent iteration of the for-loop.

Question 52

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

Answer 52

After the completion of each iteration

Question 53

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

Answer 53

Keyword ' break '

Question 54

What does the ++ increment operator do?

Answer 54

It is the shorthand equivalent to +=1

Question 55

How do you iterate through the keys of an object?

Answer 55

for...in loop

Question 56

Give 6 examples of comparison operators.

Answer 56

>, =, <=, === (strictly equal), == (loosely equal)

Question 57

What data type do comparison expressions evaluate to?

Answer 57

boolean

Question 58

What is the purpose of an if statement?

Answer 58

Lets your code do different things based on the result of a comparison

Question 59

Is else required in order to use an if statement?

Answer 59

no

Question 60

Describe the syntax (structure) of an if statement.

Answer 60

if keyword , condition, if-block, optional else-block

Question 61

What are the three logical operators?

Answer 61

&& (and), || (or), ! (not)

Question 62

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

Answer 62

Using && operator or || operator (or the ! versions)

Question 63

What is a "callback" function?

Answer 63

A function that is passed as an argument into another function. The function it’s passed into calls it later to perform some task

Question 64

Besides adding an event listener callback function to an element or the document, what is one way to delay the execution of a JavaScript function until some point in the future?

Answer 64

The setTimeout() method

Question 65

How can you set up a function to be called repeatedly without using a loop?

Answer 65

The setInterval() method

Question 66

What is the default time delay if you omit the delay parameter from setTimeout() or setInterval()?

Answer 66

Default delay is 0 (ms), meaning as soon as possible; The delay you set is the minimum amount of time elapsed before callback is run

Question 67

What do setTimeout() and setInterval() return?

Answer 67

A timer id. Use this id in clearTimeout() or clearInterval() to cancel timeout or interval

Question 68

In JavaScript, when is a function's scope determined; when it is called or when it is defined?

Answer 68

When it is defined