JavaScript Cheat Sheet

Including JavaScript in an HTML Page

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

</script>

Call an External JavaScript File

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

Including Comments

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

VARIABLES IN JAVASCRIPT

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

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True or fase statements — var c = true
Constant numbers — const PI = 3.14
Objects — var name = {firstName:"John", lastName:”Doe"}

Objects

var person = {
    firstName:"John",
    lastName:"Doe",
    age:20,
    nationality:"German"

};
THE NEXT LEVEL: ARRAYS

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

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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

OPERATORS

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

FUNCTIONS

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

JAVASCRIPT LOOPS

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 - ELSE STATEMENTS

if (condition) {
    // what to do if condition is met

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

}
STRINGS

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

REGULAR EXPRESSION SYNTAX

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

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x — Allow comments and whitespace in pattern
U — Ungreedy pattern

Brackets

[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 |

Metacharacters

. — 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

Quantifiers

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

NUMBERS AND MATH

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

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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

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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

DEALING WITH DATES IN JAVASCRIPT

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

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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.)

DOM MODE

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

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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

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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 node16 of 24

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

WORKING WITH THE USER BROWSER

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 scrolled
vertically

parent — The parent window of the current window
screen — Returns the Screen object for the window

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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

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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

JAVASCRIPT EVENTS
Mouse

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

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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 Keyboard

onkeydown — When the user is pressing a key down
onkeypress — The moment the user starts pressing a key
onkeyup — The user releases a key

Frame

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

Form

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

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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

Drag

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

Clipboard

oncopy — User copies the content of an element
oncut — The user cuts an element’s content
onpaste — A user pastes content in an element

Media

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

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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)
Animation

animationend — A CSS animation is complete
animationiteration — CSS animation is repeated
animationstart — CSS animation has started

Other

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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

Errors

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

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SyntaxError — A syntax error has occurred
TypeError — A type error has occurred
URIError — An encodeURI() error has occurred