JavaScript

Question 1

what is the purpose of variables

Answer 1

Variables are containers for storing data

Variables store data values

Question 2

How do you declare a varaible?

Answer 2

Ways to Declare a JavaScript Variable:

Using var
Using let
Using const

Question 3

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

Answer 3

To initialize (assign a value to) a variable, you use the equal sign =

Question 4

what characters are allowed in variable names?

Answer 4

variable names can’t contain spaces

variable names must begin with a letter, an underscore, or a dollar sign

variable names can contain letters, underscores, numbers, or dollar signs

variables are case sensitive

Question 5

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

Answer 5

It means that the case matters

cat =/= Cat

Question 6

What is the purpose of a string?

Answer 6

JavaScript strings are for storing and manipulating text

Question 7

what is the purpose of a number?

Answer 7

The purpose of numbers is to represent and manipulate numbers

Question 8

what is the purpose of boolean?

Answer 8

A JavaScript Boolean represents one of two values: true or false.

Very often, in programming, you will need a data type that can only have one of two values, like

YES / NO
ON / OFF
TRUE / FALSE
For this, JavaScript has a Boolean data type. It can only take the values true or false.

Question 9

what does the = operator mean in JavaScript?

Answer 9

the = operator is an assignment operator.

it assigns value to JavaScript variables

Question 10

how do you update the value of a variable?

Answer 10

You update the value of a variable by reassigning it using the assignment operator =

Question 11

what is the difference between null and undefined

Answer 11

The undefined property indicates that a variable has not been assigned a value, or not declared at all.

null is a special value that represents an empty or unknown value.

Question 12

why is it a good idea to include labels when you log values to the browser console?

Answer 12

so you know when shit dont work

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 data type is returned by arithmetic operation

Question 15

what is string concatenation?

Answer 15

string concatenation is the combining of strings

Question 16

what purpose does the addition (+) operator serve in JavaScript

Answer 16

the addition (+) can be used for arithmetic or concatenating strings

Question 17

what data type is returned by comparing two values with logical operators?

Answer 17

boolean data type is returned when comparing two operands with logical operators

Question 18

what does the addition assignment (+=) operator do?

Answer 18

the addition assignment (+=) operator assigns the result of the expression back to the first value

Question 19

what are objects used for

Answer 19

An object is a collection of related data and/or functionality.

These usually consist of variables and functions
(which are called properties and methods when they are inside objects).

Question 20

what are object properties?

Answer 20

An object is a collection of related data and/or functionality. These usually consist of several variables and functions (which are called properties and methods when they are inside objects).

Question 21

describe object literal notation

Answer 21

{
key: value
}

Question 22

How do you remove a property from an object?

Answer 22

To delete a property from an object, you can use the delete operator
Delete Object.Property
Delete person(object).name(property)

Question 23

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

Answer 23

The two ways to get or update the value of a property are dot and bracket notation

Question 24

What are arrays used for?

Answer 24

An array is a special variable, which can hold more than one value
Arrays are used to store data
Think of arrays as lists

Question 25

Describe array literal notation

Answer 25

``` Array literal notation looks like the following: var newArr = [] ```

Question 26

How are arrays different from plain objects?

Answer 26

Objects represent things with properties and methods | Array create and store lists of data in a single variable

Question 27

What number represents the first index of an array?

Answer 27

Zero is the number which represents the first index of an array Arrays are based on zero index, meaning arrays start a 0 instead of 1

Question 28

What is the length property of an array?

Answer 28

he length property of an array returns the length of an array The length is 1 indexed, meaning the count starts at 1 The length is not 0 indexed

Question 29

How do you calculate he last index of an array?

Answer 29

To calculate the last index of an array, you would use the .length property and subtract 1 You subtract 1 because .length property is 1 indexed, and arrays are 0 indexed

Question 30

What is a function in JavaScript?

Answer 30

A JavaScript function is a block of code designed to perform a particular task A JavaScript function is executed when something invokes/calls it

Question 31

Describe the parts of a function definition (when a function is being created)

Answer 31

A JavaScript function is defined with the function keyword, followed by a name followed by parentheses

Question 32

What characters are allowed for function names?

Answer 32

Function names can contain letters, digits, underscores, and dollar signs (same rule as variables)

Question 33

What can be included within the parentheses of a function definition?

Answer 33

a function definition's parentheses can contain parameters separated by commas

Question 34

Describe the parts of a function call

Answer 34

The parts of a function call include the name of the function along with any arguments that may or may not be passed

Question 35

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

Answer 35

a function definition has the function keyword preceding (coming before) the name Function definition: function sampleFunction() Function call: sampleFunction()

Question 36

Why are function parameters useful?

Answer 36

Function parameters are useful because they hint at what values should be passed in as arguments for the function

Question 37

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

Answer 37

When JavaScript reaches a return statement, the function will stop executing. Functions often compute a return value. The return value is returned back to the caller

Question 38

What is a method?

Answer 38

JavaScript methods are actions that can be performed on objects A JavaScript method is a property containing a function definition Methods are functions stored as object properties You access an object method with the following syntax: objectName.methodName()

Question 39

How is a method different from any other function?

Answer 39

A function can be called without an object A method is a function that is associated with a particular object

Question 40

How do you remove the las element from an array?

Answer 40

You can use he array.pop() method to remove elements from the end of an array

Question 41

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

Answer 41

You can round down to he nearest integer with the Math.floor() method Example: Math.floor(1.6) returns 1

Question 42

How do you generate a random number?

Answer 42

You can generate a random number with the Math.random() function Example: Math..Random(100) returns a number from 1 - 100

Question 43

How do you delete an element from an array?

Answer 43

You can use the array.splice() method to remove elements from an array You can use the array..pop() method to remove elements from the end of an array You can use the array.shift() method to remove elements from the front of an array

Question 44

How do you append an element to an array?

Answer 44

You can use the array.push() method to append an element to an array You can also use array[array.length] = value

Question 45

How do you break a string up into an array?

Answer 45

You can use the string.split() method to break a string into an array

Question 46

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

Answer 46

No, string methods do not change the original string Strings are immutable You could check by console.log('string')

Question 47

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

Answer 47

No, the return value of a function or a method is not useful in every situation, it can be excluded

Question 48

What are comparison operators?

Answer 48

Comparison operators are used in logical statements to determine equality or difference between variables or values

Question 49

Give 6 examples of comparison operators

Answer 49

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

Question 50

What data type do comparison expressions evaluate to?

Answer 50

Comparison expressions evaluate to boolean values (true or false)

Question 51

What is the purpose of an if statement?

Answer 51

If statements are used to execute specific JavaScript code blocks if a condition is true

Question 52

Is else required in order to use an if statement?

Answer 52

No

Question 53

Describe the syntax of an if statement

Answer 53

if (condition) { code to be executed if condition is true }

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

You can compare two different expressions in the same condition by wrapping the expression in parenthesis

Question 56

What is the purpose of a loop?

Answer 56

To repeat an action

Question 57

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

Answer 57

the condition expression of a loop = the brakes for the loop the purpose of the condition expression in a loop is to tell the loop when to stop (the brakes) condition - a boolean expression to be evaluated before each loop iteration. If this expression evaluates to true, the inner commands will be executed

Question 58

What does iteration mean in the context of loops?

Answer 58

Every time the loop runs through the code block

Question 59

What is a condition within the context of a for loop?

Answer 59

A condition is an expression to be evaluated before each loop iteration If this expression evaluates to true, statement is executed

Question 60

What is a statement within the context of a for loop?

Answer 60

A statement is what's contained within the opening curly brackets for the for loops' code block A statement ( code within the code block ) that is executed as long as the condition evaluates to true

Question 61

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

Answer 61

before each loop iteration

Question 62

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

Answer 62

The initialization expression of a for loop gets evaluated at the beginning ( initialization )

Question 63

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

Answer 63

before each loop iteration

Question 64

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

Answer 64

The final expression of a for loop gets evaluated after the code block / at the end

Question 65

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

Answer 65

The break statement keyword exits a loop before its condition expression evaluates to false

Question 66

what does the ++ increment operator do?

Answer 66

The increment operator ( ++ ) increments ( adds one to ) its operand ( data value ) and returns a value

Question 67

What is an operand?

Answer 67

an operand is a data value

Question 68

how do you iterate through the keys of an object?

Answer 68

you iterate through the keys of an object with a for in loop the for in loop iterates ( loops ) over the properties ( keys ) of an object The code block inside the loop is executed once for each property The properties ( keys ) are the condition. The code runs for however many keys there are

Question 69

Which document is being referred to in the phrase Document Object Model ( DOM )

Answer 69

The document object the html document

Question 70

What is a DOM tree?

Answer 70

The HTML DOM model constructed as a tree of objects ( HTML elements represented as DOM elements )

Question 71

Give two examples of document methods that retrieve a single element from the DOM

Answer 71

document.querySelector() getElementByID()

Question 72

Give one example of a document method that retrieves multiple elements from the DOM at once

Answer 72

document.querySelectorAll()

Question 73

Why might you want to assign he return value of a DOM query to a variable Why would you do this: var pElement = document.querySelector('p')

Answer 73

You might want to add/change/remove the element You might want to add/change/remove the element's attributes You might want to add/change/remove the events associated with the element or element's parent/descendants

Question 74

what console method allows you to inspect the properties of a DOM element object?

Answer 74

console.dir()

Question 75

why would a tag need to be placed at the bottom of the HTML content instead of at the top?

Answer 75

because when the browser loads the page, it must complete loading relevant JS scripts/files before loading the rest of the page. this causes a slow page load / bad UX

Question 76

what does document.querySelector() take as its argument and what does it return?

Answer 76

document.querySelector() takes CSS selectors as its argument

Question 77

What is the purpose of events and event handling?

Answer 77

to execute code when an event occurs

Question 78

what is a callback function?

Answer 78

a callback function is a function passed into another function as an argument

Question 79

what is the event.target?

Answer 79

the event.target is the location of the event trigger .target is a property of the event object

Question 80

what is the className proeprty of element objecs?

Answer 80

the className property sets or returns an element's class attribute