JS 1

Question 1

What is the purpose of variables?

Answer 1

variables are assigned data, and allow for referring to them later to access that data

Question 2

How do you declare a variable?

Answer 2

“var” or “let” keyword followed by the name

Question 3

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

Answer 3

variable name, equal sign, followed by value assigned

Question 4

What characters are allowed in variable names?

Answer 4

numbers, letters, _, $

Question 5

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

Answer 5

case (lowercase/uppercase) needs to be exact, since they are differentiated in javascript

Question 6

What is the purpose of a string?

Answer 6

a string is made up of characters in a row and is used to store text

Question 7

What is the purpose of a number?

Answer 7

a number is for numeric value and used in mathematical operations

Question 8

What is the purpose of a boolean?

Answer 8

booleans allow for the ability to make decisions based on true or false

Question 9

What does the = operator mean in JavaScript?

Answer 9

the assignment operator allows for assigning a value to a variable

Question 10

How do you update the value of a variable?

Answer 10

variable name, then equal sign, followed by new value

Question 11

What is the difference between null and undefined?

Answer 11

• null is assigned to a variable which should be purposefully empty for now
• undefined is accidentally empty, assigned by computer when no value is provided

Question 12

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

Answer 12

helps to know where the information is coming from, helps other developers

Question 13

Give five examples of JavaScript primitives.

Answer 13

string, number, boolean, null, undefined

Question 14

What data type is returned by an arithmetic operation?

Answer 14

number

Question 15

What is string concatenation?

Answer 15

combining strings with the plus operator

Question 16

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

Answer 16

adding numbers or combining strings (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

adds the result of the right side plus the left side and replaces the left side

Question 19

What are objects used for?

Answer 19

store key/value collections of data, as well as methods relevant to that object

Question 20

What are object properties?

Answer 20

the association between a key and a value, or the equivalent of a variable stored in an object

Question 21

Describe object literal notation.

Answer 21

a way to initialize an object using the left curly brace and right curly brace, with optional properties nested inside

Question 22

How do you remove a property from an object?

Answer 22

• use the delete operator to remove the property completely

- assign to empty string to remove the value only

Question 23

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

Answer 23

• dot notation: object name, dot, property key

- bracket notation: object name, brackets enclosing quotation marks enclosing property key

Question 24

What are arrays used for?

Answer 24

arrays store lists of information

Question 25

Describe array literal notation.

Answer 25

square brackets surrounding the data strings

Question 26

How are arrays different from "plain" objects?

Answer 26

arrays are ordered by number, objects have property names

Question 27

What number represents the first index of an array?

Answer 27

zero

Question 28

What is the length property of an array?

Answer 28

number of elements in an array

Question 29

How do you calculate the last index of an array?

Answer 29

array.length - 1

Question 30

What is a function in JavaScript?

Answer 30

a reusable container of code which performs actions

Question 31

Describe the parts of a function definition.

Answer 31

function keyword, function name, parameters surrounded by parenthesis, code block, optional return statement

Question 32

Describe the parts of a function call.

Answer 32

function name, arguments surrounded by parenthesis

Question 33

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

Answer 33

A function definition is the creation/declaration of the function with a function keyword and code block, while a function call is running/invoking an already created function.

Question 34

What is the difference between a parameter and an argument?

Answer 34

A parameter takes in arguments. Parameters are placeholders in a function's definition, while arguments are values used in a function's call.

Question 35

Why are function parameters useful?

Answer 35

Parameters allow for performing actions on different data of the same type when the function is invoked multiple times.

Question 36

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

Answer 36

a return statement exits the code block and allows the called function to evaluate to the returned value

Question 37

Why do we log things to the console?

Answer 37

to see an output to help debugging in development

Question 38

What is a method?

Answer 38

a function in an object

Question 39

How is a method different from any other function?

Answer 39

a method is specific to an object, so have to specify object name with method

Question 40

How do you remove the last element from an array?

Answer 40

.pop() method

Question 41

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

Answer 41

Math.floor() method

Question 42

How do you generate a random number?

Answer 42

Math.random() method

Question 43

How do you delete an element from an array?

Answer 43

.splice() method with first arg being index and second arg being number of items to remove

Question 44

How do you append an element to an array?

Answer 44

.push() method

Question 45

How do you break a string up into an array?

Answer 45

.split() method with argument being what character(s) you want to split with

Question 46

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

Answer 46

No, MDN documentation

Question 47

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

Answer 47

not always

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

``` < Less than operator. > Greater than operator. <= Less than or equal operator. >= Greater than or equal operator. !== strict inequality operator === strict equality operator ```

Question 50

What data type do comparison expressions evaluate?

Answer 50

boolean

Question 51

What is the purpose of an if statement?

Answer 51

check a condition to make choices

Question 52

Is 'else' required in order to use an if statement?

Answer 52

no

Question 53

Describe the syntax (structure) of an if statement.

Answer 53

if keyword, then condition in parenthesis, then body in curly braces

Question 54

What are the three logical operators?

Answer 54

&& and operator || or operator ! not operator

Question 55

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

Answer 55

use logical operators (&&, ||) in between the expressions

Question 56

What is the purpose of a loop?

Answer 56

repetition

Question 57

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

Answer 57

to see if the loop should stop

Question 58

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

Answer 58

an instance of repeating the code block

Question 59

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

Answer 59

before the while loop body runs

Question 60

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

Answer 60

first

Question 61

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

Answer 61

after initialization, but before code block runs

Question 62

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

Answer 62

at the end of each iteration

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 keyword

Question 64

What does the ++ increment operator do?

Answer 64

increases value of operand by 1

Question 65

How do you iterate through the keys of an object?

Answer 65

for / in loop