JavaScript (The Language of the Web) Cheat Sheet - Beginner’s essential

JavaScript (The Language of the Web) Cheat Sheet - Beginner’s essential

Published at - Aug 24, 2021

JavaScript is a cross-platform, object-oriented scripting language used to make webpages interactive (e.g., having complex animations, clickable buttons, popup menus, etc.).  There are also more advanced server-side versions of JavaScript such as Node.js, which allow you to add more functionality to a website than downloading files (such as realtime collaboration between multiple computers). Inside a host environment (for example, a web browser), JavaScript can be connected to the objects of its environment to provide programmatic control over them.

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Including JavaScript in an HTML Page

<script type="text/javascript">
//JS code goes here

Call an External JavaScript File

<script src="myscript.js"></script><code></code>

Including Comments

Single line comments - //
Multi-line comments - /* comment here */


var, const, let

var — The most common variable. Can be reassigned but only accessed within a function. Variables defined with var move to the top when code is executed.

const — Can not be reassigned and not accessible before they appear within the code.

let — Similar to const, however, let variable can be reassigned but not re-declared.

Data Types

Numbers — var age = 23

Variables — var x

Text (strings) — var a = "init"

Operations — var b = 1 + 2 + 3

True or fase statements — var c = true

Constant numbers — const PI = 3.14

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


var person = {


var fruit = ["Banana", "Apple", "Pear"];

Array Methods

concat() — Join several arrays into one

indexOf() — Returns the primitive value of the specified object

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() — Sort elements in descending order

shift() — Remove the first element of an array

slice() — Pulls a copy of a portion of an array into a new array

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 first position at which a given element appears in an array


Basic Operators

+ — Addition

- — Subtraction

* — Multiplication

/ — Division

(...) — Grouping operator, operations within brackets are executed earlier than those outside

% — Modulus (remainder )

++ — Increment numbers

-- — Decrement numbers

Comparison Operators

== — Equal to

=== — 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 Operators

&& — Logical and

|| — Logical or

! — Logical not

Bitwise Operators

& — AND statement

| — OR statement

~ — NOT

^ — XOR

<< — Left shift

>> — Right shift

>>> — Zero fill right shift


function name(parameter1, parameter2, parameter3) {
    // what the function does

Outputting Data

alert() — Output data in an alert box in the browser window

confirm() — Opens up a yes/no dialog and returns true/false depending on user click

console.log() — Writes information to the browser console, good for debugging purposes

document.write() — Write directly to the HTML document

prompt() — Creates an dialogue for user input

Global Functions

decodeURI() — Decodes a Uniform Resource Identifier (URI) created by encodeURI or similar

decodeURIComponent() — Decodes a URI component

encodeURI() — Encodes a URI into UTF-8

encodeURIComponent() — Same but for URI components

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 (before loop; condition for loop; execute after loop) {
    // what to do during the loop

for — The most common way to create a loop in JavaScript

while — Sets up conditions under which aloop executes

do while — Similar to the while loop, however, it executes at least once and performs a check at the end to see if the condition is met to execute again

break — Used to stop and exit the cycle at certain conditions

continue — Skip parts of the cycle if certain conditions are met


if (condition) {
    // what to do if condition is met
} else {
    // what to do if condition is not met


var person = "John Doe";

Escape Characters

\' — Single quote

\" — Double quote

\\ — Backslash

\b — Backspace

\f — Form feed

\n — New line

\r — Carriage return

\t — Horizontal tabulator

\v — Vertical tabulator

String Methods

charAt() — Returns a character at a specified position inside a string

charCodeAt() — Gives you the unicode of character at that position

concat() — Concatenates (joins) two or more strings into one

fromCharCode() — Returns a string created from the specified sequence of UTF-16 code units

indexOf() — Provides the position of the first occurrence of a specified text within a string

lastIndexOf() — Same as indexOf() but with the last occurrence, searching backwards

match() — Retrieves the matches of a string against a search pattern

replace() — Find and replace specified text in a string

search() — Executes a search for a matching text and returns its position

slice() — Extracts a section of a string and returns it as a new string

split() — Splits a string object into an array of strings at a specified position

substr() — Similar to slice() but extracts a substring depended on a specified number of characters

substring() — Also similar to slice() but can’t accept negative indices

toLowerCase() — Convert strings to lower case

toUpperCase() — Convert strings to upper case

valueOf() — Returns the primitive value (that has no properties or methods) of a string object


Pattern Modifiers

e — Evaluate replacement

i — Perform case-insensitive matching

g — Perform global matching

m — Perform multiple line matching

s — Treat strings as single line

x — Allow comments and whitespace in pattern

U — Ungreedy 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

\0 — NUL character

\n — A new line character

\f — Form feed character

\r — Carriage return character

\t — Tab character

\v — Vertical tab character

\xxx — The character specified by an octal number xxx

\xdd — Character specified by a hexadecimal number dd

\uxxxx — The Unicode character specified by a hexadecimal number xxxx


n+ — Matches any string that contains at least one n

n* — Any string that contains zero or more occurrences of n

n? — A string that contains zero or one occurrences of n

n{X} — String that contains a sequence of X n’s

n{X,Y} — Strings that contains a sequence of X to Y n’s

n{X,} — Matches any string that contains a sequence of at least X n’s

n$ — Any string with n at the end of it

^n — String with n at the beginning of it

?=n — Any string that is followed by a specific string n

?!n — String that is not followed by a specific string n


Number Properties

MAX_VALUE — The maximum numeric value representable in JavaScript

MIN_VALUE — Smallest positive numeric value representable in JavaScript

NaN — The “Not-a-Number” value

NEGATIVE_INFINITY — The negative Infinity value

POSITIVE_INFINITY — Positive Infinity value

Number Methods

toExponential() — Returns a string with a rounded number written as exponential notation

toFixed() — Returns the string of a number with a specified number of decimals

toPrecision() — String of a number written with a specified length

toString() — Returns a number as a string

valueOf() — Returns a number as a number

Math Properties

E — Euler’s number

LN2 — The natural logarithm of 2

LN10 — Natural logarithm of 10

LOG2E — Base 2 logarithm of E

LOG10E — Base 10 logarithm of E

PI — The number PI

SQRT1_2 — Square root of 1/2

SQRT2 — The square root of 2

Math Methods

abs(x) — Returns the absolute (positive) value of x

acos(x) — The arccosine of x, in radians

asin(x) — Arcsine of x, in radians

atan(x) — The arctangent of x as a numeric value

atan2(y,x) — Arctangent of the quotient of its arguments

ceil(x) — Value of x rounded up to its nearest integer

cos(x) — The cosine of x (x is in radians)

exp(x) — Value of Ex

floor(x) — The value of x rounded down to its nearest integer

log(x) — The natural logarithm (base E) of x

max(x,y,z,...,n) — Returns the number with the highest value

min(x,y,z,...,n) — Same for the number with the lowest value

pow(x,y) — X to the power of y

random() — Returns a random number between 0 and 1

round(x) — The value of x rounded to its nearest integer

sin(x) — The sine of x (x is in radians)

sqrt(x) — Square root of x

tan(x) — The tangent of an angle


Setting Dates

Date() — Creates a new date object with the current date and time

Date(2017, 5, 21, 3, 23, 10, 0) — Create a custom date object. The numbers represent year, month, day, hour, minutes, seconds, milliseconds. You can omit anything you want except for year and month.

Date("2017-06-23") — Date declaration as a string

Pulling Date and Time Values

getDate() — Get the day of the month as a number (1-31)

getDay() — The weekday as a number (0-6)

getFullYear() — Year as a four digit number (yyyy)

getHours() — Get the hour (0-23)

getMilliseconds() — The millisecond (0-999)

getMinutes() — Get the minute (0-59)

getMonth() — Month as a number (0-11)

getSeconds() — Get the second (0-59)

getTime() — Get the milliseconds since January 1, 1970

getUTCDate() — The day (date) of the month in the specified date according to universal time (also available for day, month, fullyear, hours, minutes etc.)

parse — Parses a string representation of a date, and returns the number of milliseconds since January 1, 1970

Set Part of a Date

setDate() — Set the day as a number (1-31)

setFullYear() — Sets the year (optionally month and day)

setHours() — Set the hour (0-23)

setMilliseconds() — Set milliseconds (0-999)

setMinutes() — Sets the minutes (0-59)

setMonth() — Set the month (0-11)

setSeconds() — Sets the seconds (0-59)

setTime() — Set the time (milliseconds since January 1, 1970)

setUTCDate() — Sets the day of the month for a specified date according to universal time (also available for day, month, fullyear, hours, minutes etc.)


Node Properties

attributes — Returns a live collection of all attributes registered to and element

baseURI — Provides the absolute base URL of an HTML element

childNodes — Gives a collection of an element’s child nodes

firstChild — Returns the first child node of an element

lastChild — The last child node of an element

nextSibling — Gives you the next node at the same node tree level

nodeName — Returns the name of a node

nodeType — Returns the type of a node

nodeValue — Sets or returns the value of a node

ownerDocument — The top-level document object for this node

parentNode — Returns the parent node of an element

previousSibling — Returns the node immediately preceding the current one

textContent — Sets or returns the textual content of a node and its descendants

Node Methods

appendChild() — Adds a new child node to an element as the last child node

cloneNode() — Clones an HTML element

compareDocumentPosition() — Compares the document position of two elements

getFeature() — Returns an object which implements the APIs of a specified feature

hasAttributes() — Returns true if an element has any attributes, otherwise false

hasChildNodes() — Returns true if an element has any child nodes, otherwise false

insertBefore() — Inserts a new child node before a specified, existing child node

isDefaultNamespace() — Returns true if a specified namespaceURI is the default, otherwise false

isEqualNode() — Checks if two elements are equal

isSameNode() — Checks if two elements are the same node

isSupported() — Returns true if a specified feature is supported on the element

lookupNamespaceURI() — Returns the namespaceURI associated with a given node

lookupPrefix() — Returns a DOMString containing the prefix for a given namespaceURI, if present

normalize() — Joins adjacent text nodes and removes empty text nodes in an element

removeChild() — Removes a child node from an element

replaceChild() — Replaces a child node in an element

Element Methods

getAttribute() — Returns the specified attribute value of an element node

getAttributeNS() — Returns string value of the attribute with the specified namespace and name

getAttributeNode() — Gets the specified attribute node

getAttributeNodeNS() — Returns the attribute node for the attribute with the given namespace and name

getElementsByTagName() — Provides a collection of all child elements with the specified tag name

getElementsByTagNameNS() — Returns a live HTMLCollection of elements with a certain tag name belonging to the given namespace

hasAttribute() — Returns true if an element has any attributes, otherwise false

hasAttributeNS() — Provides a true/false value indicating whether the current element in a given namespace has the specified attribute

removeAttribute() — Removes a specified attribute from an element

removeAttributeNS() — Removes the specified attribute from an element within a certain namespace

removeAttributeNode() — Takes away a specified attribute node and returns the removed node

setAttribute() — Sets or changes the specified attribute to a specified value

setAttributeNS() — Adds a new attribute or changes the value of an attribute with the given namespace and name

setAttributeNode() — Sets or changes the specified attribute node

setAttributeNodeNS() — Adds a new namespaced attribute node to an element


Window Properties

closed — Checks whether a window has been closed or not and returns true or false

defaultStatus — Sets or returns the default text in the statusbar of a window

document — Returns the document object for the window

frames — Returns all <iframe> elements in the current window

history — Provides the History object for the window

innerHeight — The inner height of a window’s content area

innerWidth — The inner width of the content area

length — Find out the number of <iframe> elements in the window

location — Returns the location object for the window

name — Sets or returns the name of a window

navigator — Returns the Navigator object for the window

opener — Returns a reference to the window that created the window

outerHeight — The outer height of a window, including toolbars/scrollbars

outerWidth — The outer width of a window, including toolbars/scrollbars

pageXOffset — Number of pixels the current document has been scrolled horizontally

pageYOffset — Number of pixels the document has been scrolledvertically

parent — The parent window of the current window

screen — Returns the Screen object for the window

screenLeft — The horizontal coordinate of the window (relative to screen)

screenTop — The vertical coordinate of the window

screenX — Same as screenLeft but needed for some browsers

screenY — Same as screenTop but needed for some browsers

self — Returns the current window

status — Sets or returns the text in the statusbar of a window

top — Returns the topmost browser window

Window Methods

alert() — Displays an alert box with a message and an OK button

blur() — Removes focus from the current window

clearInterval() — Clears a timer set with setInterval()

clearTimeout() — Clears a timer set with setTimeout()

close() — Closes the current window

confirm() — Displays a dialogue box with a message and an OK and Cancelbutton

focus() — Sets focus to the current window

moveBy() — Moves a window relative to its current position

moveTo() — Moves a window to a specified position

open() — Opens a new browser window

print() — Prints the content of the current window

prompt() — Displays a dialogue box that prompts the visitor for input

resizeBy() — Resizes the window by the specified number of pixels

resizeTo() — Resizes the window to a specified width and height

scrollBy() — Scrolls the document by a specified number of pixels

scrollTo() — Scrolls the document to specified coordinates

setInterval() — Calls a function or evaluates an expression at specified intervals

setTimeout() — Calls a function or evaluates an expression after a specified interval

stop() — Stops the window from loading

Screen Properties

availHeight — Returns the height of the screen (excluding the Windows Taskbar)

availWidth — Returns the width of the screen (excluding the Windows Taskbar)

colorDepth — Returns the bit depth of the color palette for displaying images

height — The total height of the screen

pixelDepth — The color resolution of the screen in bits per pixel

width — The total width of the screen



onclick — The event occurs when the user clicks on an element

oncontextmenu — User right-clicks on an element to open a context menu

ondblclick — The user double-clicks on an element

onmousedown — User presses a mouse button over an element

onmouseenter — The pointer moves onto an element

onmouseleave — Pointer moves out of an element

onmousemove — The pointer is moving while it is over an element

onmouseover — When the pointer is moved onto an element or one of its children

onmouseout — User moves the mouse pointer out of an element or one of its children

onmouseup — The user releases a mouse button while over an element


onkeydown — When the user is pressing a key down

onkeypress — The moment the user starts pressing a key

onkeyup — The user releases a key


onabort — The loading of a media is aborted

onbeforeunload — Event occurs before the document is about to be unloaded

onerror — An error occurs while loading an external file

onhashchange — There have been changes to the anchor part of a URL

onload — When an object has loaded

onpagehide — The user navigates away from a webpage

onpageshow — When the user navigates to a webpage

onresize — The document view is resized

onscroll — An element’s scrollbar is being scrolled

onunload — Event occurs when a page has unloaded


onblur — When an element loses focus

onchange — The content of a form element changes (for <input>, <select>and <textarea>)

onfocus — An element gets focus

onfocusin — When an element is about to get focus

onfocusout — The element is about to lose focus

oninput — User input on an element

oninvalid — An element is invalid

onreset — A form is reset

onsearch — The user writes something in a search field (for <input="search">)

onselect — The user selects some text (for <input> and <textarea>)

onsubmit — A form is submitted


ondrag — An element is dragged

ondragend — The user has finished dragging the element

ondragenter — The dragged element enters a drop target

ondragleave — A dragged element leaves the drop target

ondragover — The dragged element is on top of the drop target

ondragstart — User starts to drag an element

ondrop — Dragged element is dropped on the drop target


oncopy — User copies the content of an element

oncut — The user cuts an element’s content

onpaste — A user pastes content in an element


onabort — Media loading is aborted

oncanplay — The browser can start playing media (e.g. a file has buffered enough)

oncanplaythrough — When browser can play through media without stopping

ondurationchange — The duration of the media changes

onended — The media has reach its end

onerror — Happens when an error occurs while loading an external file

onloadeddata — Media data is loaded

onloadedmetadata — Meta data (like dimensions and duration) are loaded

onloadstart — Browser starts looking for specified media

onpause — Media is paused either by the user or automatically

onplay — The media has been started or is no longer paused

onplaying — Media is playing after having been paused or stopped for buffering

onprogress — Browser is in the process of downloading the media

onratechange — The playing speed of the media changes

onseeked — User is finished moving/skipping to a new position in the media

onseeking — The user starts moving/skipping

onstalled — The browser is trying to load the media but it is not available

onsuspend — Browser is intentionally not loading media

ontimeupdate — The playing position has changed (e.g. because of fast forward)

onvolumechange — Media volume has changed (including mute)

onwaiting — Media paused but expected to resume (for example, buffering)


animationend — A CSS animation is complete

animationiteration — CSS animation is repeated

animationstart — CSS animation has started Other


transitionend — Fired when a CSS transition has completed

onmessage — A message is received through the event source

onoffline — Browser starts to work offline

ononline — The browser starts to work online

onpopstate — When the window’s history changes

onshow — A <menu> element is shown as a context menu

onstorage — A Web Storage area is updated

ontoggle — The user opens or closes the <details> element

onwheel — Mouse wheel rolls up or down over an element

ontouchcancel — Screen touch is interrupted

ontouchend — User finger is removed from a touch screen

ontouchmove — A finger is dragged across the screen

ontouchstart — Finger is placed on touch screen


try — Lets you define a block of code to test for errors

catch — Set up a block of code to execute in case of an error

throw — Create custom error messages instead of the standard JavaScript errors

finally — Lets you execute code, after try and catch, regardless of the result

Error Name Values

name — Sets or returns the error name

message — Sets or returns an error message in string from

EvalError — An error has occurred in the eval() function

RangeError — A number is “out of range”

ReferenceError — An illegal reference has occurred

SyntaxError — A syntax error has occurred

TypeError — A type error has occurred

URIError — An encodeURI() error has occurred

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