prep-javascript-variables, objects, and arrays

Question 1

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

Answer 1

The = (equals) operator in JavaScript is an assignment operator. It assigns the value of the variable(s) on the right side of the = (equals) operator to the variable on the left side of the = (equals) operator.

Question 2

Which keyword is used to declare a variable in JavaScript?

Answer 2

var, let, or const

Question 3

Which characters is a JavaScript variable allowed to begin with?

Answer 3

A letter, $, or _

Question 4

What are quotation marks used for in JavaScript?

Answer 4

To create string values

Question 5

What is the purpose of strings in JavaScript?

Answer 5

To hold text values like “John Doe” in a variable,

and

JavaScript strings are for storing and manipulating text.

Question 6

What is the purpose of booleans in JavaScript?

Answer 6

JavaScript booleans are often used to find out if an expression or variable is true or not

Ex: “Boolean(10 > 9)” would return the boolean value of “true”.

Question 7

What is the purpose of numbers in JavaScript?

Answer 7

The purpose of numbers in JavaScript is to store numeric values (decimal and non-decimal) in variables.
Arithmetic operations can be performed on these variables that hold numeric values such as addition, subtraction, division, modulo, etc.

Question 8

What does null mean in JavaScript?

Answer 8

“null” means an object has no value.
An object can be assigned “null” to show that it has no value.
This is different from “undefined” because “undefined” means that a value has not been set for a variable when the variable was declared.

Question 9

What data types can object properties hold?

Answer 9

strings, numbers, arrays, booleans, functions

Question 10

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

Answer 10

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

The syntax of object-literals consists of the use of the keyword “const” followed by the variable name; and it is assigned the properties and property values to the right of the equal (=) sign operator, which are separated by commas inside curly braces.

Question 11

What is the principal use of arrays?

Answer 11

To store “list” type data in a numerically indexed data structure, which is zero-indexed.

Question 12

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

Answer 12

const array_name = [item 1, item 2, …];

Question 13

What number represents the first index of an array?

Answer 13

0

Question 14

How can you access the last element of an array?

Answer 14

lastElement = myArray[myArray.length - 1];