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JavaScript Cheat Sheet

lakpa profile image LP ・16 min read

JavaScript Basics
Let’s start off with the basics – how to include JavaScript in a website.

Including JavaScript in an HTML Page
To include JavaScript inside a page, you need to wrap it in tags:</p> <script type="text/javascript"> //JS code goes here

With this input, the browser can identify and execute the code properly.

Call an External JavaScript File
You can also place JavaScript in its own file and name it inside your HTML. That way, you can keep different types of code separate from one another, making for better-organized files. If your code is in a file called myscript.js, you would call it:


Including Comments
Comments are important because they help other people understand what is going on in your code or remind you if you forgot something yourself. Keep in mind that they have to be marked properly so the browser won’t try to execute them.

In JavaScript you have two different options:

Single-line comments — To include a comment that is limited to a single line, precede it with //
Multi-line comments — In case you want to write longer comments between several lines, wrap it in /* and */ to avoid it from being executed
Variables in JavaScript
Variables are stand-in values that you can use to perform operations. You should be familiar with them from math class.

var, const, let
You have three different possibilities for declaring a variable in JavaScript, each with their own specialties:

var — The most common variable. It can be reassigned but only accessed within a function. Variables defined with var move to the top when the code is executed.
const — Can not be reassigned and not accessible before they appear within the code.
let — Similar to const, the let variable can be reassigned but not re-declared.
Data Types
Variables can contain different types of values and data types. You use = to assign them:

Numbers — var age = 23
Variables — var x
Text (strings) — var a = "init"
Operations — var b = 1 + 2 + 3
True or false statements — var c = true
Constant numbers — const PI = 3.14
Objects — var name = {firstName:"John", lastName:"Doe"}
There are more possibilities. Note that variables are case sensitive. That means lastname and lastName will be handled as two different variables.

Objects
Objects are certain kinds of variables. They are variables that can have their own values and methods. The latter are actions that you can perform on objects.

var person = {
firstName:"John",
lastName:"Doe",
age:20,
nationality:"German"
};
The Next Level: Arrays
Next up in our JavaScript cheat sheet are arrays. Arrays are part of many different programming languages. They are a way of organizing variables and properties into groups. Here’s how to create one in JavaScript:

var fruit = ["Banana", "Apple", "Pear"];
Now you have an array called fruit which contains three items that you can use for future operations.

Array Methods
Once you have created arrays, there are a few things you can do with them:

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() — Sort elements in a 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 primitive value of the specified object
Operators
If you have variables, you can use them to perform different kinds of operations. To do so, you need 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 JavaScript functions are blocks of code that perform a certain task. A basic function looks like this:

function name(parameter1, parameter2, parameter3) {
// what the function does
}
As you can see, it consists of the function keyword plus a name. The function’s parameters are in the brackets and you have curly brackets around what the function performs. You can create your own, but to make your life easier – there are also a number of default functions.

Outputting Data
A common application for functions is the output of data. For the output, you have the following options:

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 a dialogue for user input
Global Functions
Global functions are functions built into every browser capable of running JavaScript.

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
Loops are part of most programming languages. They allow you to execute blocks of code desired number of times with different values:

for (before loop; condition for loop; execute after loop) {
// what to do during the loop
}
You have several parameters to create loops:

for — The most common way to create a loop in JavaScript
while — Sets up conditions under which a loop executes
do while — Similar to the while loop but 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
These types of statements are easy to understand. Using them, you can set conditions for when your code is executed. If certain conditions apply, something is done, if not – something else is executed.

if (condition) {
// what to do if condition is met
} else {
// what to do if condition is not met
}
A similar concept to if else is the switch statement. However, using the switch you select one of several code blocks to execute.

Strings
Strings are what JavaScript calls to text that does not perform a function but can appear on the screen.

var person = "John Doe";
In this case, John Doe is the string.

Escape Characters
In JavaScript, strings are marked with single or double-quotes. If you want to use quotation marks in a string, you need to use special characters:

\' — Single quote
\" — Double quote
Aside from that you also have additional escape characters:

\ — Backslash
\b — Backspace
\f — Form feed
\n — New line
\r — Carriage return
\t — Horizontal tabulator
\v — Vertical tabulator
String Methods
There are many different ways to work with strings:

charAt() — Returns a character at a specified position inside a string
charCodeAt() — Gives you the Unicode of a 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 backward
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 depending 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
Regular expressions are search patterns used to match character combinations in strings. The search pattern can be used for text search and text to replace operations.

Pattern Modifiers
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 the pattern
U — Ungreedy pattern
Brackets
[abc] — Find any of the characters between the brackets
[^abc] — Find any character which is 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 occurrence of n
n{X} — String that contains a sequence of X n’s
n{X,Y} — Strings that contain 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 ni
Numbers and Math
In JavaScript, you can also work with numbers, constants and perform mathematical functions.

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 the 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
Dealing with Dates in JavaScript
You can also work with and modify dates and time with JavaScript. This is the next chapter in the JavaScript cheat sheet.

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 a year, month, day, hour, minutes, seconds, milliseconds. You can omit anything you want except for a 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, full year, 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, full year, hours, minutes etc.)
DOM Mode
The DOM is the Document Object Model of a page. It is the code of the structure of a webpage. JavaScript comes with a lot of different ways to create and manipulate HTML elements (called nodes).

Node Properties
attributes — Returns a live collection of all attributes registered to an 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 namespace URI associated with a given node
lookupPrefix() — Returns a DOMString containing the prefix for a given namespace URI 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
Working with the User Browser
Besides HTML elements, JavaScript is also able to take into account the user browser and incorporate its properties into the code.

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 status bar of a window
document — Returns the document object for the window
frames — Returns all 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 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
screenLeft — The horizontal coordinate of the window (relative to the 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 status bar 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 Cancel button
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
JavaScript Events
Events are things that can happen to HTML elements and are performed by the user. The programming language can listen for these events and trigger actions in the code. No JavaScript cheat sheet would be complete without them.

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
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 , and )
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 )
onselect — The user selects some text (for and )
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 the 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 — The browser can play through media without stopping
ondurationchange — The duration of the media changes
onended — The media has reached its end
onerror — Happens when an error occurs while loading an external file
onloadeddata — Media data is loaded
onloadedmetadata — Metadata (like dimensions and duration) are loaded
onloadstart — The 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 — The 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 — The 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
transitionend — Fired when a CSS transition has completed
onmessage — A message is received through the event source
onoffline — The browser starts to work offline
ononline — The browser starts to work online
onpopstate — When the window’s history changes
onshow — A element is shown as a context menu
onstorage — A Web Storage area is updated
ontoggle — The user opens or closes the element
onwheel — Mouse wheel rolls up or down over an element
ontouchcancel — Screen-touch is interrupted
ontouchend — User’s finger is removed from a touch-screen
ontouchmove — A finger is dragged across the screen
ontouchstart — A finger is placed on the touch-screen
Errors
When working with JavaScript, different errors can occur. There are several ways of handling them:

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
JavaScript also has a built-in error object. It has two properties:

name — Sets or returns the error name
message — Sets or returns an error message in a string from
The error property can return six different values as its name:

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
The JavaScript Cheat Sheet in a Nutshell
JavaScript is gaining much importance as a programming language. It is increasingly the go-to language for building web properties thanks to its proven track record and benefits.

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@lakpa

I once single-highhandedly defended a small village in the Amazon Basin from a horde of ferocious army ants using only a hoe and a large glass of water

Discussion

pic
Editor guide
 

Nice content, but my eyes are bleeding :D

 

It's perfect but if there was color for keywords may be a lot better keep going

 

Good content but, but one thing bugged me ... why did you tag you're post as Java content ... this is not Java but JavaScript ^^

 

I guess the same reason Javascript was renamed from Livescript - To gain popularity 😂

 

I'm guessing this was copy/pasted from somewhere that had formatting.

Like maybe here:
websitesetup.org/javascript-cheat-...

 

It is make simple and very clean. Good effort