JavaScript

Question 1

Adding comments to your JavaScript

Answer 1

// for a single line comment

/* this is for a multiline comment */

Question 2

How to declare value to a variable

Answer 2

var x = 5

here x is the variable and 5 is the value

Question 3

Printing to the log

Answer 3

console.log()

Question 4

The five primitive types

Answer 4

Number - Numberical values
String - Characters surrounded by single or double quotes
Boolean - true or false statements
Null - a variable that doesn’t have a value - this is delibrate!! You have to phyically name something null.
Undefined - a variable that is missing a value - NOT delibrate!

Question 5

infinity and NaN

Answer 5

these are defined as numbers! not strings!!!

NaN means not a number lol

Question 6

Some operating actions

Answer 6

+ Addition/Concatenation 5 + 4 9
- Subtraction 8 - 1 7
* Multiplication 6 * 7 42
% Modulu (remainder) 10 % 3 1
** Exponent 2**4 16

Question 7

Adding numbers and Concatenating string

Answer 7

var x = 5
var y = 6
var z = "hello"
var a = "world"
console.log(x = y)
prints 11
console.log(z + a)
prings "helloworld"
console.log(z + " " + a)
prings "hello world"

Question 8

String Interpolation

Answer 8

Use backticks instead of quotes!!

var name = 'Tris'
var age = 7
var sentence = 'I'm ${name} and I'm ${age} !'
console.log(sentence)
prints "I'm Tris and I'm 7!"

Question 9

Statements vs Expressions

Answer 9

Statements are instructions
var x = 1000 - this statment defines a value
console.log(‘hi’) - this statement logs a value
Expressions resolves to a value
x == y - expression that evaluates to false
15 + 2 - expression that evaluates to 17

(in a statment you’re telling the computer something. in an expression you’re asking the computer to answer something)

Question 10

What is a Boolean Expression?

Answer 10

Expressions that resolve to a Boolean data type (true/false)

Question 11

8 comparison operators

Answer 11

== Abstract equality (can compare things that don’t have the same primitive type
i.e. 1 == “1” where 1 is a number and “1” is a string)
!= Abstract inqueality (same as above but it’s telling you two things are NOT
equal
=== Strict equality (these HAVE to be the same primitive type)
!== Strict inqueality
< Less than
<= Less th an or equal to
> Greater than
>= Greater than or equal to

Question 12

True or False? Anything that isn’t falsy is truthy

Answer 12

TRUE!!!!

Question 13

True or False? NaN = NaN

Answer 13

FALSE! NaN means not a number. But they are not neccessarily the same NaN
Think of it like two differnt secrets
Or how a lion and a napkin are both not numbers but a lion isn’t equal to a napkin

Question 14

if Statement example

Answer 14

if (boolean expression) {
code to run if expression is true
}

if (isLoggedIn) {
console.log(“User is logged in.”)
}

Question 15

else if statement example

Answer 15

if (false) {
   This won't run.
} else if (true) {
   This will run.
}

if(userAge > 21) {
   console.log("User is an adult.")
} else if(userAge >12) {
   console.log("User is a teenager.")
}

Question 16

else statement example

Answer 16

if(false) {
   This won't run
} else {
   This will run
}

if(isLoggedIn) {
   console.log("User is logged in.")
   // show profile page
} else {
   console.log("User is not loggedf in.")
   /// show sign in page
}

Question 17

switch statemnet example

Answer 17

switch(variable) {
   case value 1:
      code to run if variable is equal to value 1
   break
   case value 2
      code to run if variable is equal to value 2
   break
}

let currentPage = “home”

switch(currentPage) {
   case 'home':
      console.log('Display the homepage.')
//this will run
   break
   case 'profile'"
      console.log('Display the profile page.') 
//this will not run
   break
}

Question 18

switch default statement example

Answer 18

switch(variable) {
case value 1:
code to run if variable is equal to value 1
break
case value 2:
code to run if variable is equal to value 2
break
default:
code to run if variable doesn’t equal value 1 or 2
break
}

let currentPage = “foo”

switch(currentPage) {
   case 'home':
      console.log('Display the homepage.')
//this will not run
   break
   case 'profile':
      console.log('Display the profile page.')
//this will not run
   break
   default:
      console.log('Display a "page not found" error.')
//THIS WILL RUN! HOORAY
   break
}

Question 19

Array

Answer 19

a variable that stores multiple elements

Question 20

Concatenation

Answer 20

combining multiple strings

Question 21

Iteration

Answer 21

Repeating a process (lines of code)

Helpful for processing every element in an array

Question 22

What is a For Loop & The Anatomy of a For Loop

Answer 22

A way to iterate. Loops can run code a number of times

Initializer
Condition
Aferthought

for(let x = 0; x < 4; x++) {
      console.log(x)
}

Question 23

Initializer

Answer 23

Runs before the loop! Tells us where to start the loop

Question 24

Condition

Answer 24

Boolean expression that stops the loop when the answer is false. Without this, it would go on forever.

Question 25

Afterthought

Answer 25

Runs at the end of each cycle in the loop. It tells the code how to move from the start of the loop to the next piece

Question 26

Body (in forLoops)

Answer 26

The code to execute until the condition is false

Question 27

let card = {
   number: 9
}

identify the object, the property, and the value

Answer 27

object: card
property: number
value: 9

Question 28

Functions and their properties

Answer 28

a block of code designed to perfom task
funtions must have
  - function name
  - pair of parentheses
  - pair of curly braces

Question 29

Calling a function

Answer 29

To call a function, write only the name with a pair of parenthese

function sayHi ( ) {
     console.log("Hello!")
}

sayHi ( ) is the function

Question 30

Parameters

Answer 30

allow inputs to the function
you can have as many as you want
used to put new value inside parenthese when calling a function

Question 31

Return Statements

Answer 31

the function stops executing and goes back to where the function was called

Question 32

Scope

Global vs Local

Answer 32

The place in your code where a variable is defined

Global: The scope that contains all other scopes; all variables defined here are visible in all contained scopes
Local: An isolated scope typically defined by curly braces. All variables defined here are only visible within the scope itself

Question 33

Dot notation

Answer 33

A way to access properties of an object using “.”