JavaScript

Question 1

What is the purpose of variables?

Answer 1

To store/see data that came together from the past & preserve data to use in the future

Question 2

How do you declare a variable?

Answer 2

By using let, const or var

Question 3

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

Answer 3

By using the assignment operator to give it value

Question 4

What characters are allowed in variable names?

Answer 4

Letter
Underscore
$
numbers (but it cannot be the first character)

Question 5

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

Answer 5

Capitalized and lowercase letters mean different things

Question 6

What is the purpose of a string?

Answer 6

To store a series of characters

Question 7

What is the purpose of a number?

Answer 7

To perform math

To represent numeric values

Question 8

What is the purpose of a boolean?

Answer 8

To make decisions

Question 9

What does the = operator mean in JavaScript?

Answer 9

To make it hold/contain a value

Question 10

How do you update the value of a variable?

Answer 10

By assigning a new value

Question 11

What is the difference between null and undefined?

Answer 11

Null is intentional absence/emptiness

Undefined means there is no value assigned

Question 12

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

Answer 12

To make it easy to know which value the console is printing

Question 13

Give five examples of JavaScript primitives.

Answer 13

Boolean
Null
Number
String
Undefined 

(and BigInt and Symbol)

Question 14

What data type is returned by an arithmetic operation?

Answer 14

Numeric/number

Question 15

What is string concatenation?

Answer 15

To join/append strings

Question 16

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

Answer 16

To add numbers or to concatenate strings

Question 17

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

Answer 17

Boolean

Question 18

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

Answer 18

Adds the value on the right side of the operator to the variable and assigns the result back to the variable

Question 19

What are objects used for?

Answer 19

To group together a set of properties and methods

Question 20

What are object properties?

Answer 20

Chunk of data attached to objects

Question 21

Describe object literal notation

Answer 21

var variableName = {
key : value,
key : value
}

Question 22

How do you remove a property from an object?

Answer 22

With the delete operator

Question 23

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

Answer 23

By using dot notation or square brackets

Question 24

What are arrays used for?

Answer 24

For storing a list of values

Question 25

Describe array literal notation

Answer 25

arrayname[‘value’, ‘value’];

Question 26

How are arrays different from "plain" objects?

Answer 26

There is an order They are numerically indexed It keeps a count of the number of values in it

Question 27

What number represents the first index of an array?

Answer 27

0

Question 28

What is the length property of an array?

Answer 28

It’s a property that returns the number of values in that array

Question 29

How do you calculate the last index of an array?

Answer 29

arrayName.length - 1

Question 30

What is a function in JavaScript?

Answer 30

Reusable block of code

Question 31

Describe the parts of a function definition.

Answer 31

``` function optName(parameters) { block of code to run optional return keyword }; ```

Question 32

Describe the parts of a function call:

Answer 32

functionName( );

Question 33

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

Answer 33

- No function keyword | - No curly braces and code block

Question 34

What is the difference between a parameter and an argument?

Answer 34

Parameter is a placeholder name Argument is the value that actually gets passed

Question 35

Why are function parameters useful?

Answer 35

They give us an idea of what kind of value were looking to put in the argument

Question 36

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

Answer 36

1. Produces a value | 2. Ends the code block from running

Question 37

Why do we log things to the console?

Answer 37

- To see change over time | - As a debugging mechanism

Question 38

What is a method?

Answer 38

Function stored in a property | function that is the property of an object

Question 39

How is a method different from any other function?

Answer 39

They are attached to objects (so you have to specify the object name)

Question 40

How do you remove the last element from an array?

Answer 40

.pop()

Question 41

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

Answer 41

Math.floor()

Question 42

How do you generate a random number?

Answer 42

Math.random()

Question 43

How do you delete an element from an array?

Answer 43

.splice(index, how many items to remove)

Question 44

How do you append (add to end) an element to an array?

Answer 44

.push()

Question 45

How do you break a string up into an array?

Answer 45

.split()

Question 46

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

Answer 46

No (strings are immutable) | console.log()

Question 47

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

Answer 47

No because sometimes you're interested in simply what the function/method does and not its return value

Question 48

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

Answer 48

MDN

Question 49

Give 6 examples of comparison operators

Answer 49

``` == === != !== < ><= >= ```

Question 50

What data type do comparison expressions evaluate to?

Answer 50

Boolean

Question 51

What is the purpose of an if statement?

Answer 51

Make a decision on which code block to run depending on the Boolean result

Question 52

Is else required in order to use an if statement?

Answer 52

No – you don’t always need an alternative

Question 53

Describe the syntax (structure) of an if statement.

Answer 53

``` if (condition) { statement1; } else { statement2; } ```

Question 54

What are the three logical operators?

Answer 54

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

Question 55

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

Answer 55

By using logical operators && or ||

Question 56

What is the purpose of a loop?

Answer 56

To keep executing a code as long as a condition runs true

Question 57

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

Answer 57

To let the function know when to end

Question 58

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

Answer 58

One execution of code block

Question 59

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

Answer 59

In the beginning before the code block executes

Question 60

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

Answer 60

In the beginning before anything

Question 61

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

Answer 61

Before each iteration

Question 62

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

Answer 62

After the code block is executed

Question 63

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

Answer 63

break

Question 64

What does the ++ increment operator do?

Answer 64

adds 1 to value

Question 65

How do you iterate through the keys of an object?

Answer 65

for...in loop

Question 66

What must the return value of myFunction be if the following expression is possible? myFunction()();

Answer 66

A function! | myFunction is being called and the return is being called immediately

Question 67

What does this code do? const wrap = value => () => value;

Answer 67

Defines a function that defines the value and defines another function that returns that value

Question 68

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

Answer 68

Defined

Question 69

What allows JavaScript functions to "remember" values from their surroundings?

Answer 69

Closures

Question 70

What does fetch() return?

Answer 70

A Promise If you get back a promise what do you do with it? You can call .then OR .catch on it

Question 71

What is the default request method used by fetch()?

Answer 71

GET

Question 72

How do you specify the request method (GET, POST, etc.) when calling fetch?

Answer 72

fetch('string of resource', { method: 'GET' })