JavaScript Basics

Question 1

What is the principal use of arrays?

Answer 1

to store ordered lists of data

Question 2

Describe the syntax (structure) of array-literals in JavaScript.

Answer 2

var array_name = [item1, item2, item3,…] ;

Question 3

How can you access the last element of an array?

Answer 3

const fruits = [“Banana”, “Orange”, “Apple”, “Mango”];

let fruit = fruits[fruits.length - 1];

Question 4

What data types can object properties hold?

Answer 4

booleans
strings
numbers
undefined
null

Question 5

Describe the syntax (structure) of object-literals in JavaScript.

Answer 5

var person = {firstName:”John”, lastName:”Doe”, age:50, eyeColor:”blue”};

Question 6

What does the = (equals) operator do in JavaScript?

Answer 6

assignment operator: assigns the value to a variable

**does NOT mean “equal to”

Question 7

Which keyword is used to declare a variable in JavaScript?

Answer 7

var
let
const

Question 8

Which characters is a JavaScript variable allowed to begin with?

Answer 8

upper or lowercase letter
$ dollar sign
_ underscore

Question 9

What are quotation marks used for in JavaScript?

Answer 9

text strings

Question 10

What is the purpose of variables?

Answer 10

to store data values

Question 11

What is the purpose of strings in JavaScript?

Answer 11

storing & manipulating text

Question 12

What is the purpose of booleans in JavaScript?

Answer 12

logic to represent 1 of 2 values

true/false
on/off
yes/no

Question 13

What is the purpose of numbers in JavaScript?

Answer 13

to represent and manipulate numbers

Question 14

definition:

Null vs Undefined

Answer 14

null - intentional absence of any OBJECT value (put there by programmer as ex/ var nothing = null)

undefined - value never assigned (default value of variable ex/ var never)

Question 15

What is the purpose of objects?

Answer 15

To group together set of variables and fxns to create a model of something from real world

Question 16

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

Answer 16

dot notation
bracket notation (substitutions)

Question 17

variables & memory location

objects & memory location

Answer 17

REFERENCE (objects) !== PRIMITIVES

var a = b
b can sometimes =/ a

obj a = obj b
they are the same because they are pointing to same memory address (and modifying that address)

Question 18

What data type do comparison expressions evaluate to?

Answer 18

booleans

Question 19

Give 6 examples of comparison operators.

Answer 19

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

Question 20

What is the purpose of an if statement?

Answer 20

evaluates to a boolean

conditionally run code based on boolean value of expression

Question 21

Describe the syntax (structure) of an if statement.

Answer 21

if (condition) {
run code
}