JavaScript Cheat Sheet & Quick Guide

var

The most common variable. Var variables move to the top when code is executed

const

A variable that cannot be reassigned and is not accessible before they appear within the code

let

The let variable can be reassigned but not re-declared

var age = 23

Numbers

var x

Variables

var a = “init”

Text (strings)

var b = 1 + 2 + 3

Operations

var c = true

True or false statements

const PI = 3.14

Constant numbers

var name = {firstName:”John”, lastName:”Doe”}

Objects

concat()

Join several arrays into one

indexOf()

Returns the first position at which a given element appears in an array

join()

Combine elements of an array into a single string and return the string

lastIndexOf()

Gives the last position at which a given element appears in an array

pop()

Removes the last element of an array

push()

Add a new element at the end

reverse()

Reverse the order of the elements in an array

shift()

Remove the first element of an array

slice()

Pulls a copy of a portion of an array into a new array of 4 24

sort()

Sorts elements alphabetically

splice()

Adds elements in a specified way and position

toString()

Converts elements to strings

unshift()

Adds a new element to the beginning

valueOf()

Returns the primitive value of the specified object

(plus sign) +

Addition

–

Subtraction

*

Multiplication

/

Division

(..) Grouping operator

Grouping operator

%

Remainder

(two plus signs) ++

Increment numbers

—

Decrement numbers

( 2 equal signs) ==

Equal to

(3 equal signs) ===

Equal value and equal type

!=

Not equal

!==

Not equal value or not equal type

>

Greater than

<

Less than

>=

Greater than or equal to

<=

Less than or equal to

?

Ternary operator

&&

Logical and

!!

Logical or

!

Logical not

&

AND statement

|

OR statement

~

NOT

^

XOR

<<

Left shift

>>

Right shift

>>>

Zero fill right shift

alert()

An alert box is displayed with an OK button

confirm()

Displays a message box with ok/cancel options

console.log()

Writes information to the browser 

document.write()

Write directly to the HTML document

prompt()

A pop up box that needs user input

decodeURI()

Decodes a Uniform Resource Identifier (URI) created by encodeURI 

decodeURIComponent()

Decodes a URI component

encodeURI()

Encodes a URI into UTF-8

encodeURIComponent()

Encodes a URI using numbers to represent letters

eval()

Evaluates JavaScript code represented as a string

isFinite()

Determines whether a passed value is a finite number

isNaN()

Determines whether a value is NaN or not

Number()

Returns a number converted from its argument

parseFloat()

Parses an argument and returns a floating point number

parseInt()

Parses its argument and returns an integer

for

The most common way to create a loop in JavaScript

while

Sets up conditions for a loop

do-while

Checks once again to see if the conditions are met

break

Stops the loop cycle if conditions aren’t met

continue

Skip parts of the loop if conditions are met

if (condition) {//}

If a condition is met do this

} else {//}

If a condition is not met do this

‘

Single quote

“

Double quote

Backslash

b

Backspace

f

Form feed

n

Newline

r

Carriage return

t

Horizontal tabulator

v

Vertical tabulator

charAt()

Returns a character at a specified position

charCodeAt()

Gives you the unicode of character at a specified position

concat()

Joins multiple strings together

fromCharCode()

Converts UTF-16 unicode values to characters

indexOf()

Returns the position of the first occurrence of a specified element

lastIndexOf()

Returns the position of the last occurrence of a specified element

match()

Returns any matches of a string 

replace()

Find and replace specific text

search()

Searches for text and returns its position

slice()

Extracts a section of a string and returns it

split()

Splits a string into substrings and returns it at a specified position

substr()

Extracts a string and returns it at a specified position

substring()

Excluding negative indices, splits a string into substrings and returns it at a specified position 

toLowerCase()

Convert to lowercase

toUpperCase()

Convert to uppercase

valueOf()

Returns the primitive value of a string object

e

Evaluate replacement

i

Perform case-insensitive matching

g

Perform global matching

m

Perform multiple line matching

s

Treat strings as a single line

x

Allow comments and whitespace in pattern

U

Non Greedy pattern

[abc]

Find any of the characters between the brackets

[^abc]

Find any character not in the brackets

[0-9]

Used to find any digit from 0 to 9

[A-z]

Find any character from uppercase A to lowercase z

(a|b|c)

Find any of the alternatives separated with |

.

Find a single character, except newline or line terminator

w

Word character

W

Non-word character

d

A digit

D

A non-digit character

s

Whitespace character

S

Non-whitespace character

b

Find a match at the beginning/end of a word

B

A match not at the beginning/end of a word