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JavaScript Cheat Sheet for Web Development?

JavaScript Cheat Sheet for Web Development?

JavaScript is a programming language mostly used by web developers to create web pages and applications to provide an interactive and dynamic user experience. Most of the web-based applications and functions that make the Internet vital to modern-day life are coded in JavaScript in form or another.

JavaScript is an old language as it started in the late 1990s. The fact that JavaScript is currently used by 94.5% of all websites highlights the importance of JavaScript as a programming language. Being a client-side programming language, JavaScript helps web developers to create websites dynamic and interactive by implementing the custom scripts.

Simultaneously, the web developers also use cross-platform runtime software like Node.js to write server-side codes in JavaScript. Web developers can even put up a combination of JavaScript, HTML5, and CSS3 to create web pages that work across various browsers, platforms, and devices. There are also several other reasons which make JavaScript a must-have tool under the belt for modern-day web developers to get all benefits of it.

This article is intended to work as a Web Development boot camp to understand and learn JavaScript. We will go through the JavaScript cheat sheet to facilitate young aspirants of web development.

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JavaScript Cheat Sheet

Basics

Including JavaScript in HTML Page

To include JavaScript inside a web page, wrap it in <script> tags

<script type="text/javascript">

 

 //Add JS code here

 

</script>

 

Including External JavaScript File

JavaScript can also be placed in its own file and be named it inside HTML

<script src="filename.js"></script>

 

Adding Comments

Comments let other people understand what is going on in your code or remind you if you forget something.

One line comments: //

Multi-line comments: /* comment here */

 

Variables

Variables are those values that you can use to perform operations

var, const, let

There are three different possibilities for using a variable in JavaScript with their unique specialties:

var: The most common variable. Can be reallocated but only accessible within a function.

Const: Can’t be reassigned and not accessible before appearing within the code.

let: Just like const, however, let variable can be reassigned

 

Data Types

Variables contain different types of values and data types which are assigned by using =

Numbers: var age = 25

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:”Wick"}

 

Objects

These are certain kinds of variables with their own values and methods

var student = {

    firstName:"John",

    lastName:"Wick",

    age:25,

    nationality:"British"

};

Arrays

Arrays are part of several programming languages. They are used to organize variables and properties into groups

var dogs = ["Poodle", " Bulldog ", "Labrador"];

 

Array Methods

Once arrays have been created, there are a few things you can experiment with them

concat( ): Join various arrays into one

indexOf( ): Returns the first position of given element at which it appears in an array

join( ): Combine elements of an array into a single string and return it

lastIndexOf( ): Gives the last position of given element at which it appears in an array

pop( ): Eliminates the last element of an array

push( ): Add 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

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Operators

Operators are used for performing different operations with variables

Basic Operators

+ : Addition

- : Subtraction

*: Multiplication

/ : Division

(...) : Grouping. Operations within brackets are executed first

%: Modulo (remainder )

++ : Postfix Increment

-- :  Postfix Decrement

 

Comparison Operators

== : Equal to

=== : Both equal value and type

!= : Not equal

!== : Neither equal value nor 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

| : OR

~ : NOT

^ : XOR

<< : Left Shift

>> : Right Shift

>>> : Zero Fill Right Shift

 

Functions

In JavaScript functions are blocks of code to perform a certain task. A basic function may look like as under:

function name(parameter1, parameter2, parameter3) {

 // function role

}

 

The function’s parameters are given in the brackets. Moreover, the task of a function is written in curly brackets.

Output of Data

Functions are commonly used for the output of data. For the output, the following options are available:

alert() : Display data in an alert box

confirm() : Opens up a yes/no dialogue box and returns true/false depending on user response

console.log() : Transcribes information to the browser console

document.write() : Transcribes directly to the HTML document

prompt() : User input dialogue box

 

Global Functions

Global functions are universal functions which are built into every browser capable of running JavaScript:

decodeURI() : Decodes a Uniform Resource Identifier (URI) produced by encodeURI

decodeURIComponent() : Decodes a URI component

encodeURI() : Encodes URI into UTF-8

encodeURIComponent() : Same as above but for URI components

eval() : Evaluates JS code presented as a string

isFinite() : Defines if a passed value is a finite number

isNaN() : Defines whether a value is NaN or otherwise

Number() : Returns a number transformed from its argument

parseFloat() : Analyzes an argument and returns a floating-point number

parseInt() : Analyzes its argument and returns an integer

 

JS Loops

Loops are included in most programming languages. They allow developers to execute blocks of code several times with different values:

for (before loop; condition for loop; execute after loop) {

    // what to do within the loop

}

 

Some parameters to create loops are:

for : The most used way to create a loop in JS

while : Lay down conditions under which a loop executes

do while : Similar to the while loop but it executes at least once

break : Used to stop and exit the cycle at specific conditions

continue : Skip parts of the cycle if specific conditions are fulfilled

 

If – Else Statements

Easily understandable, using these statements, you can set conditions for when your code is executed

if (condition) {

    // what to do if condition is fulfilled

} else {

    // what to do if condition is not fulfilled

}

 

Strings

Strings in JS are the text that does not perform any function but can appear on the screen

var person = "John Wick";

 

Escape Characters

In JS, if you want to use quotation marks within a string, you need to use special 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

There are several ways to use strings

\charAt() : Returns a character to a specified position

charCodeAt() : Provides the Unicode of a character at that position

concat() : Concatenates (connects) two or more strings

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

indexOf() : Provides the position of the first incidence of a specified text within a string

lastIndexOf() : Same as above but with the last occurrence

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

replace() : Find and replace specific text in a string

search() : Executes a search for a matching text

slice() : Extracts a section of a string as a new string

split() : Splits a string object into an collection of strings

substr() :  Similar to slice() but extracts a substring

substring() : Like slice() but can’t accept negative guides

toLowerCase() : Change strings to lower case

toUpperCase() : Change strings to upper case

valueOf() : Returns the original value of a string object

 

Regular Expression Syntax

These are search patterns used to match character combinations in strings

Pattern Modifiers

e : Evaluates a replacement

i : Carry out case-insensitive matching

g : Carry out global matching

m : Performs multiple line matching

s : Treats strings as a single line

x : Allow comments in the pattern

 

Meta-characters

. : Find a single character

\w : Word character

\W : Non-word character

\d : A digit

\D : A non-digit character

\s : Whitespace character

\S : Non-whitespace character

\b : A match at the beginning or end of a word

\B : A match not at the beginning or 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 : Unicode character specified by a hexadecimal number XXXX

 

Quantifiers

n+ : Matches any string with at least one n

n* : String with zero or more occurrences of n

n? : String with zero or one occurrence of n

n{X} : String with 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 with a sequence of at least X n’s

n$ : 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

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Numbers and Math

In JS, you can perform mathematical functions.

Number Properties

MAX_VALUE : Maximum numeric value

MIN_VALUE : Smallest positive numeric value

NaN : “Not-a-Number” value

NEGATIVE_INFINITY : Negative Infinity value

POSITIVE_INFINITY : Positive Infinity value

 

Number Methods

toExponential() : Returns the string with a rounded number

toFixed() : Returns the string 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 : 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 positive value of x

acos(x) : The arccosine of x

asin(x) : Arcsine of x

atan(x) : Arctangent of x as a numeric value

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

cos(x) : The cosine of x in radians

exp(x) : Value of Ex

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

pow(x,y) : X to the power of Y

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

tan(x) : Tangent of an angle

 

Dates in JS

JS also allows people to work with date and time

Setting Date

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

Date(2020, 7, 13, 2, 45, 10, 0) : Custom date object with a year, month, day, hour, minutes, seconds, milliseconds

Date("2020-07-13") : Date as a string

Date and Time Values

getDate() : Day of the month (1-31)

getDay() :  Weekday as a number (0-6)

getFullYear() : Year (yyyy)

getHours() : Hour (0-23)

getMinutes() : Minute (0-59)

getMonth() :  Month as a number (0-11)

getUTCDate() : The day (date) of the month according to universal time

 

User Browser

JS is also enabled to take into account the user browser and incorporate the properties in the code.

Window Properties

closed : Whether a window has been closed or not

defaultStatus : Sets or returns the default text in the status

frames : All <iframe> elements in the current window

history : Provides the History object for the window

innerHeight : Inner height of content area

innerWidth : Inner width of content area

length : 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

outerHeight : Outer height including toolbars/scrollbars

outerWidth : Outer width including toolbars/scrollbars

pageXOffset : Number of pixels horizontally

pageYOffset : Number of pixels vertically

parent : Parent window of the current window

screenLeft : Horizontal coordinate of the window

screenTop : Vertical coordinate of the window

self : Returns the current window

 

Window Methods

alert() : Displays an alert box

close() : Closes the current window

confirm() : Dialogue box with an OK and Cancel button

open() : Opens new browser window

print() : Prints the content

prompt() : Dialogue box for visitor’s input

stop() : Stops the window from loading

 

JS Events

In JS, Events are things which can happen to HTML elements as performed by the user.

Mouse

onclick :When the user clicks on an element

oncontextmenu : User right-clicks on an element

ondblclick : Double click on an element

onmousedown : User presses a mouse button over an element

onmouseenter : Pointer moves onto an element

onmouseleave : Pointer moves away from an element

onmouseup : User releases a mouse button while over an element

 

Keyboard

onkeydown : User pressing a key down

onkeypress : When user starts pressing a key

onkeyup : User releases a key

 

Frame

onabort : Loading of a media is terminated

onbeforeunload : It occurs before the document is about to be unloaded

onerror : Error while loading an external file

onhashchange : Changes to the anchor part of a URL

onload : Object has loaded

onpagehide : User go away from a webpage

onpageshow : User comes to a webpage

onresize : Document view is resized

onscroll : Element’s scrollbar is scrolled

onunload : It occurs when a page has unloaded

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Form

onblur : An element loses focus

onchange : The content of a form element changes

onfocus : Element gets focus

onfocusin : When an element is about to get focus

onfocusout : Element is about to lose focus

oninput : User input on an element

oninvalid : Element is invalid

onreset : A form is reset

onsearch : User enters something in a search field

onselect : Text selection by user

onsubmit : Form is submitted

 

Drag

ondrag : When element is dragged

ondragend : User has completed dragging the element

ondragenter : Dragged element gets a drop target

ondragleave : Dragged element leaves the drop target

ondragover : Dragged element comes on top of the drop target

ondragstart : User starts to drag an element

ondrop : Dragged element is dropped on the target

 

Clipboard

oncopy : Content of an element copied by the user

oncut : User cuts an element’s content

onpaste : Content is pasted by the user

 

Media

onabort : Loading is cancelled

oncanplay : Media can start playing by browser

ondurationchange : Duration of the media changes

onerror : While loading an external file error occurs

onloadeddata : Date of media is loaded

onloadstart :  Browser looks for specified media

onpause : Media is paused

onplay : The media is on play

onprogress : Media is downloading by browser

onseeking : User starts moving / skipping

onsuspend : Browser is deliberately not loading media

ontimeupdate : Media playing position has changed

onvolumechange : Change in media volume (including mute)

onwaiting : Media paused but likely to resume (e.g., buffering)

 

Animation

animationend : CSS animation has been completed

animationiteration : CSS animation has been repeated

animationstart : CSS animation has started

 

Others

transitionend : Dismissed on a CSS transition completion

onmessage : Message is received via event source

onoffline : Browser starts working offline

ononline : Browser starts working online

onpopstate : Window’s history changes

onshow : A <menu> element is displayed as a context menu

onstorage : Web Storage area has been updated

ontoggle : The <details> element is opened or closed by user

onwheel : Mouse wheel scrolls up or down above an element

ontouchcancel : Screen-touch has been disturbed

ontouchend : User’s finger is detached from a touch-screen

ontouchmove : A finger has been dragged on the screen

ontouchstart : Touch of finger is placed on the screen

 

Errors

In JS, different errors can occur and there are several ways of coping with them

try : Allows you set up a block of code for testing errors

catch : Define a block of code to execute in case of an error

throw : Instead of the standard JS errors it creates custom error messages

finally : Allows you execute code irrespective of the result, after try and catch method

 

Errors Names & Values

JS also has a built-in error object with a couple of properties:

name : Sets or yields the name of error

message : Sets or returns an error message in a form of string

The error property can result in six different values:

EvalError : Error occurs in the eval() function

RangeError : Number is “out of range”

ReferenceError : An prohibited reference has happened

SyntaxError : A syntax error has happened

TypeError : A typo error has happened

URIError : encodeURI() error has occurred

 

The JavaScript Cheat Sheet – Final Word

JavaScript, since its inception, has been continuously gaining importance as a programming language. In the JavaScript cheat sheet compiled above, most of the basic and essential functions, operators, principles, and methods have been explained. It provides a holistic overview of the language and can be taken as a reference for developers and new learners.

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