Javascript p1

Question 1

What is the purpose of variables?

Answer 1

temporarily store data

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

= assignment operator

Question 4

What characters are allowed in variable names?

Answer 4

letters, numbers, $ and _

Question 5

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

Answer 5

same var name in upper and lowercase are two dif variables

Question 6

What is the purpose of a string?

Answer 6

to manage text data

Question 7

What is the purpose of a number?

Answer 7

to manage numeric data

Question 8

What is the purpose of a boolean?

Answer 8

to work with true/false, yes/no, on/off states

Question 9

What does the = operator mean in JavaScript?

Answer 9

assignment, this var is that value

Question 10

How do you update the value of a variable?

Answer 10

reassign it

Question 11

What is the difference between null and undefined?

Answer 11

• • undefined has been declared and is unused (empty field)

- - null is intentionally empty

Question 12

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

Answer 12

so you know exactly what you’re looking at

Question 13

Give five examples of JavaScript primitives.

Answer 13

string, number, boolean, null, undefined, symbol, bigint

Question 14

What data type is returned by an arithmetic operation?

Answer 14

numeric

Question 15

What is string concatenation?

Answer 15

combining strings using the + operator

Question 16

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

Answer 16

• • combining the values it’s between

- - arithmatic & string concatenation

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

combines given values and reassigns to original variable

Question 19

code read: 
var area = width * height;

Answer 19

there’s the expression width * height, and the result of that expression is being assigned to the variable area

Question 20

code read:

motto += ‘ is the goat’;

Answer 20

the string ‘ is the goat’ is being concatenated with the variable motto and the result is being reassigned to the variable motto

Question 21

What are objects used for?

Answer 21

• • creating models of things
• • conceptualizing an idea of a thing by listing it’s attributes as properties/keys with values, so that information about it can be accessed or manipulated

Question 22

What are object properties?

Answer 22

the variables that make up the object

Question 23

Describe object literal notation.

Answer 23

– declare var name, assign it to curbrace enclosed list of comma-separated key:value pairs

var object = {
property/key: 'value',
property/key: 'value',
}

Question 24

How do you remove a property from an object?

Answer 24

• • delete object.property/key;

- - delete object[‘property’];

Question 25

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

Answer 25

• • object.property = ‘newValue’; (dot notation)

- - object[‘property’] = ‘newValue’; (square bracket syntax)

Question 26

code read:
var object = {
property: value
}

Answer 26

there is a new object literal being assigned the variable object, with the property property assigned the value value

Question 27

What are arrays used for?

Answer 27

storing a list of values

Question 28

Describe array literal notation.

Answer 28

var array = [item01, item02, item03];

Question 29

How are arrays different from “plain” objects?

Answer 29

list of index#/value pairs, not a list of key/value pairs

Question 30

What number represents the first index of an array?

Answer 30

0 zero

Question 31

What is the length property of an array?

Answer 31

array.length

Question 32

How do you calculate the last index of an array?

Answer 32

(array.length - 1)

Question 33

code read:
var colors = ['red', 'white', 'blue'];

Answer 33

there is an array literal being defined with the values of string red, string white, and string blue and assigned to the variable colors

Question 34

What is a function in JavaScript?

Answer 34

• • a bundle of code which takes arguments and processes them in some manner
• • repeatable code we can call anytime

Question 35

Describe the parts of a function definition.

Answer 35

function keyword, name (optional), parameters, code block, return statement (optional)

Question 36

Describe the parts of a function call.

Answer 36

function name, argument(s)

Question 37

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

Answer 37

• • call is small, definition has a codeblock

- - function keyword + parameters vs function’s name + arguments

Question 38

What is the difference between a parameter and an argument?

Answer 38

• • parameter is where arguments go

- - parameter = placeholder, argument = actual

Question 39

Why are function parameters useful?

Answer 39

declares/defines potential arguments

Question 40

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

Answer 40

• • causes the function to produce a value

- - exists the function

Question 41

code read:
function \_\_\_(\_\_\_) {
var \_\_ = \_\_\_ * 2;
return \_\_\_;
}
var \_\_\_ = \_\_\_(\_\_\_);

Answer 41

line one, there is a function being defined named ___, it takes a single parameter of ___, then the opening curbrace for the codeblock.
line two, there’s the expression ____, the result being assigned to var ___.
line three, ___ is being returned.
line four, closing curbrace.
line five, the ___ function is being called with the single argument of ____, and the return is being assigned to the variable ___.

Question 42

Why do we log things to the console?

Answer 42

to see what we’re doing

Question 43

What is a method?

Answer 43

• • a function that’s a property of an object

- - an object reference to a function

Question 44

How is a method different from any other function?

Answer 44

• • it’s unique to it’s object ?

- - .method() instead of function()

Question 45

How do you remove the last element from an array?

Answer 45

• • .pop() removes last and returns it

- - .shift() removes first

Question 46

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

Answer 46

• • .floor()

- - math.round()

Question 47

How do you generate a random number?

Answer 47

• • math.random()

- - math.floor(math.random() * max)

Question 48

How do you delete an element from an array?

Answer 48

.splice(start, deleteCount, item1, item2…)

myArray.splice(start, deleteCount) actually removes the element, reindexes the array, and changes its length.

delete myArray[0]
delete will delete the object property, but will not reindex the array or update its length. Note that it is not in fact set to the value undefined, rather the property is removed from the array, making it appear undefined.

Question 49

How do you append an element to an array?

Answer 49

• • .push() adds to the end of an array

- - .unshift() adds to beginning of array

Question 50

How do you break a string up into an array?

Answer 50

• • .split(‘’)

- - .join(‘’)

Question 51

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

Answer 51

• • no

- - console.log(string)

Question 52

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

Answer 52

lots, 50+

Question 53

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

Answer 53

no

Question 54

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

Answer 54

lots, 50+

Question 55

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

Answer 55

MDN

Mozilla Dev Network

Question 56

Give 6 examples of comparison operators.

Answer 56

• • > greater than
• • < less than
• • > = greater than or equal to
• • <= less than or equal to
• • == equal
• • === strictly equal value & type
• • !== not equal value or type
• • != not equal

Question 57

What data type do comparison expressions evaluate to?

Answer 57

boolean (t/f)

Question 58

What is the purpose of an if statement?

Answer 58

– to do a thing if a condition is met, otherwise do something else

The if statement executes a statement if a specified condition is truthy. If the condition is falsy, another statement can be executed.

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 (condition) {
statement1
} else {
statement2
}

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 logical operators

Question 63

What is the purpose of a loop?

Answer 63

to iterate/loop through data, such as an array

Question 64

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

Answer 64

to determine whether to execute the statement

Question 65

What does “iteration” mean in the context of loops?

Answer 65

to increase an initial value, run a check using that value, then progress to next value and repeat

Question 66

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

Answer 66

before each loop, before executing the statement

Question 67

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

Answer 67

once at the start

Question 68

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

Answer 68

at the start of each loop

Question 69

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

Answer 69

before the condition is evaluated

Question 70

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

Answer 70

break

Question 71

What does the ++ increment operator do?

Answer 71

adds +1 to the expression

Question 72

How do you iterate through the keys of an object?

Answer 72

for (const property in object)

– for…in loop