JavaScript Cheat Sheet & Quick Guide


Whether you’re still learning Javascript or are an advanced developer, it can be helpful to keep a reference sheet for common JavaScript commands. We’ve compiled a downloadable JavaScript cheat sheet to keep near your desk.

But first, let’s recap what JavaScript is and how it works. 

What is JavaScript?

JavaScript is a programming language used to create interactive elements of a website, like maps, scrolling videos, and animation. It works in tandem with other coding languages, like HTML and CSS.

What is the Difference Between JavaScript, HTML, and CSS?

JavaScript, HTML, and CSS are all programming languages with major differences: 

  • HTML is the language used to define text and headings, as well as embed images on a webpage.
  • CSS is the language used to apply styling to the HTML content, like colors and fonts. 
  • JavaScript is the language that creates interactive and dynamic content like moving graphics, maps, scrolling videos, and more. 

Where JavaScript Sits on Your Website

JavaScript sits in the HTML of your webpages. It needs to be bookended by <script> tags. For example:

<script type=”text/javascript”>

//JS code goes here

</script>

You can also add your JavaScript to a file and link to it within your HTML code. This form of linking, referred to sometimes as “linking JavaScript externally,” helps you keep track of your code.

How to Write JavaScript

There are categories of JavaScript code, including:

  • Variables: A variable is an element that can vary (i.e. a data value that can be changed.)
  • Operators: As with other programming languages, an operator operates single or multiple data values to produce a result.
  • Functions: A function takes an input and produces a related output. This is usually a set of statements that performs a task to produce a result.
  • Loops: This loops a block of code until certain conditions are met.
  • If – Else Statements: Like a flowchart, If-Else Statements run blocks of code if certain conditions are true. If the conditions are false, another block of code is run.
  • Strings: Strings are a way to store text. In strings, the first character is 0, the second character is 1, the third character is 2, and so on.
  • Regular Expressions: Also called a rational expression, a regular expression is a string of characters in a pattern used to match character combinations.
  • Numbers and Math: Numbers and Math are static properties for mathematical constants and functions.
  • Dates: As the name suggests, dates in JavaScript are a moment in time that can be as specific as a particular millisecond on any particular day.
  • DOM Node: A DOM node is a way to allow JavaScript to dynamically update the content of a page.
  • Events: An event is any change or update to the webpage that occurs as of JavaScript code being run.

JavaScript Command Cheat Sheet

When working with JavaScript, try our complete ‘cheat sheet’ of JavaScript commands. 

Variables

These are elements that can vary, which can include variables, data types, and arrays.

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

Operators

These are single or multiple data values used to produce a result, including Basic Operators, Comparison Operators, Logical Operators, and Bitwise Operators.

(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

Functions

These perform a task to produce a related output, including Outputting Data and Global Functions.

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

Loops

These occur until certain conditions are met.

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 – Else Statements

These are designed to run blocks of code if certain conditions are met.

if (condition) {//}

If a condition is met do this

} else {//}

If a condition is not met do this

Strings

These store text and include escape characters and string methods.

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

Regular Expressions 

These are patterns, including pattern modifiers, brackets, metacharacters, and quantifiers.

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

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

The 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

Numbers and Maths

These are mathematical functions, including number properties, number methods, math properties, and math methods.

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

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()

A string of a number written with a specified length

toString()

Returns a number as a string

valueOf()

Returns a number as a number

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

The square root of 1/2

SQRT2

The square root of 2

abs(x)

Returns the absolute (positive) value of x

Dates

These include specific points in time and include setting dates, and pulling date and time values, and set part of a date.

tan(x)

The tangent of an angle

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

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

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 Node

This allows JavaScript to update the web page and include node properties, node methods, and element methods.

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

appendChild()

Adds a new child node to an element as the last child node

cloneNode()

Clones a 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

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

Events

These are the updates caused by JavaScript code and include mouse, keyboard, frame, form, drag, clipboard, media, animation, and other.

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

The user presses a mouse button over an element

onmouseenter

The pointer moves onto an element

onmouseleave

The 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

The 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 reached its end

onerror

Happens when an error occurs while loading an external file

onloadeddata

Media data is loaded

onloadedmetadata

Meta 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

Browser is in the process of downloading the media

onratechange

The playing speed of the media changes

onseeked

The 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

transitionend

Fired when a CSS transition has been completed

Errors

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

An <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

The 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

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

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 <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

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

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 specific 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

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

Access this complete list in our downloadable reference chart. 

How to Identify JavaScript Issues

JavaScript errors are common, and you should address them as soon as you can. Even if there are no coding errors, there may be issues with your JavaScript that cause slow page load times, such as unminifed JavaScript

You can identify these issues by performing an audit of your site. Third-party tools like the Site Audit tool can identify issues like unminified JavaScript and site speed so that you can work on fixing them. 

To use the Site Audit tool, you’ll need to create a project for your domain. If you already have a project created for your domain, read further to learn how to configure and run the tool.

Start by logging into your Semrush account. If you don’t have an existing account, you can create a free account. Just remember that the Site Audit provides limited functionality for Free Accounts.

Once you’re in, select “Dashboard” under “Management” to be taken to your project dashboard:

Graphical user interface, text, application, email Description automatically generated

If you already have a project set up for your domain, you’ll see your project dashboard. Select the “Site Audit” card at the top of the page:

Graphical user interface, application Description automatically generated

Once the tool is open, you’ll need to configure the audit’s settings, including the crawl scope, any website restrictions, and more. Once you’re happy with the settings, select “Start Site Audit:”

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Once the audit is completed, you can navigate to the Site Audit’s dashboard for a complete overview of your audit. Navigate to the Issues tab for a list of site issues. 

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From there, you can filter the issues for any related to unminified JavaScript: 

javascript cheat sheet

Although search engines are not able to render and see JavaScript elements, fixing JS-related issues like page speed can help you perform better in search engine rankings. 

Final Thoughts

JavaScript is an important coding language that can help you transform the feel and function of your web pages. More importantly, good JavaScript code can help your website’s rankings by maintaining or improving page load speed.

Use our cheat sheet above to keep track of the most common JavaScript commands, and try third-party tools like the Site Audit to stay on top of your Javascript code when necessary. 

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