JavaScript Objects CheatSheets, Operators & Quantifiers

The JavaScript language itself, as a format, is free, and the use of JavaScript in a website is not necessarily. JavaScript Cheatsheets contain useful code examples on a single page. … Find code for JS loops, variables, JavaScript objects, data types, strings, events, and many.

Javascript is the most popular programming language in the world and that makes it a programmer’s great choice. Once you learned Javascript, it helps you developing great front-end as well as back-end software using different Javascript-based frameworks like jQuery, Node.JS, etc.

JavaScript in an HTML Page

<script type="text/javascript">

//JS code goes here

</script>

Call an External JavaScript File

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

Including Comments

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

var, const, let

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

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"}

Objects

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

Arrays

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

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

Escape Characters

\' — Single quote
\" — Double quote
\\ — Backslash
\b — Backspace
\f — Form feed
\n — New line
\r — Carriage return
\t — Horizontal tabulator
\v — Vertical tabulator

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

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

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 |

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

Some Notes

In JavaScript, it’s just NOT possible to have a reference from one variable to another variable. And, only compound values (Object, Array) can be assigned by reference. Bottom line: The typeof value assigned to a variable decides whether the value is stored with assign-by-value or assign-by-reference.

Javascript has 3 data types that are passed by reference: Array, Function, and Object. These are all technically Objects, so we’ll refer to them collectively as Objects.

To include an external JavaScript file, we can use the script tag with the attribute src. You’ve already used the src attribute when using images. The value for the src attribute should be the path to your JavaScript file. This script tag should be included between the tags in your HTML document.

Happy Coding using JavaScript Objects 🙂