Javascript Cheat Sheet Github

A quick reference to JavaScript.

Git; HTML Cheat-sheet Forms. JavaScript Cheat-sheet Arrays. Array.from(arrayLike, mapFn, thisArg) creates mapped array from array-like iterable object. Array.prototype.includes(valueToFind, fromIndex) returns true if value found. GitHub - mbeaudru/modern-js-cheatsheet: Cheatsheet for the JavaScript knowledge you will frequently encounter in modern projects. Modern JavaScript Cheatsheet Introduction Motivation Complementary Resources Table of Contents Notions Variable declaration: var, const, let Short explanation Sample code Detailed explanation var let const External resource Arrow function Sample code Detailed explanation Concision this reference Useful resources Function default parameter value External resource.

Created on: 2019-09-30

Tag: cheat_sheet

Warning

under heavy construction and not well organized

to get the last char of the string:

(source: https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_slice6)

to merge two json object:

OR:

(source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in)

output:

(source: https://www.howtogeek.com/251807/how-to-enable-pasting-text-on-sites-that-block-it/)

(source: http://nathangiesbrecht.com/check-all-checkboxes-chrome-javascript)

(auther: Sk Imtiaz Ahmed source: https://www.facebook.com/groups/desperatelyseekingbracu/permalink/2235744283319547/?comment_id=2235785336648775&comment_tracking=%7B%22tn%22%3A%22R%22%7D)

Type the fisrt part of the URL the press Shift+Delete

(source: https://productforums.google.com/forum/#!msg/chrome/i8HqLSSePLo/C0C_otXyB90J)

document.body.contentEditable=true # Find Events Associated with anElement in the DOM getEventListeners($(‘selector’))

(source: https://medium.freecodecamp.com/10-tips-to-maximize-your-javascript-debugging-experience-b69a75859329#.b6w50oyma)

run when the password manager is open from the chrome console (hit f12 to access the console) in frame settings (passwords):

~alogsinb

to go back to previous page:

source: https://stackoverflow.com/a/34178688/5350059

to check a button by class name:

source: https://stackoverflow.com/questions/25587762/javascript-click-on-element-by-class

to auto-fill user name and pass from bookmark:

source: IppSec Bitlab Youtube Video

to sleep for millisecond:

source: https://stackoverflow.com/a/39914235/5350059

to highlights all links on a webpage:

make a bookmark with:

source: https://superuser.com/a/296578

Above diagram created using Regulex

This blog post gives an overview of regular expression syntax and features supported by JavaScript. Examples have been tested on Chrome/Chromium console (version 81+) and includes features not available in other browsers and platforms. Assume ASCII character set unless otherwise specified. This post is an excerpt from my JavaScript RegExp book.

Elements that define a regular expression🔗

Note	Description
MDN: Regular Expressions	MDN documentation for JavaScript regular expressions
`/pat/`	a RegExp object
`const pet = /dog/`	save regexp in a variable for reuse, clarity, etc
`/pat/.test(s)`	Check if given pattern is present anywhere in input string
returns `true` or `false`
`i`	flag to ignore case when matching alphabets
`g`	flag to match all occurrences
`new RegExp('pat', 'i')`	construct RegExp from a string
second argument specifies flags
use backtick strings with `${}` for interpolation
`source`	property to convert RegExp object to string
helps to insert a RegExp inside another RegExp
`flags`	property to get flags of a RegExp object
`s.replace(/pat/, 'repl')`	method for search and replace
`s.search(/pat/)`	gives starting location of the match or `-1`
`s.split(/pat/)`	split a string based on regexp

Anchors	Description
`^`	restricts the match to start of string
`$`	restricts the match to end of string
`m`	flag to match the start/end of line with `^` and `$` anchors
`r`, `n`, `u2028` and `u2029` are line separators
dos-style files use `rn`, may need special attention
`b`	restricts the match to start/end of words
word characters: alphabets, digits, underscore
`B`	matches wherever `b` doesn't match

^, $ and are metacharacters in the above table, as these characters have special meaning. Prefix a character to remove the special meaning and match such characters literally. For example, ^ will match a ^ character instead of acting as an anchor.

Feature	Description
`pat1\|pat2\|pat3`	multiple regexp combined as OR conditional
each alternative can have independent anchors
`(pat)`	group pattern(s), also a capturing group
`a(b\|c)d`	same as `abd\|acd`
`(?:pat)`	non-capturing group
`(?<name>pat)`	named capture group
`.`	match any character except line separators
`[]`	Character class, matches one character among many

Greedy Quantifiers	Description
`?`	match `0` or `1` times
`*`	match `0` or more times
`+`	match `1` or more times
`{m,n}`	match `m` to `n` times
`{m,}`	match at least `m` times
`{n}`	match exactly `n` times
`pat1.*pat2`	any number of characters between `pat1` and `pat2`
`pat1.pat2\|pat2.pat1`	match both `pat1` and `pat2` in any order

Greedy here means that the above quantifiers will match as much as possible that'll also honor the overall regexp. Appending a ? to greedy quantifiers makes them non-greedy, i.e. match as minimally as possible. Quantifiers can be applied to literal characters, groups, backreferences and character classes.

Character class	Description
`[ae;o]`	match any of these characters once
`[3-7]`	range of characters from `3` to `7`
`[^=b2]`	negated set, match other than `=` or `b` or `2`
`[a-z-]`	`-` should be first/last or escaped using to match literally
`[+^]`	`^` shouldn't be first character or escaped using
`[]]`	`]` and should be escaped using
`w`	similar to `[A-Za-z0-9_]` for matching word characters
`d`	similar to `[0-9]` for matching digit characters
`s`	similar to `[ tnrfv]` for matching whitespace characters
use `W`, `D`, and `S` for their opposites respectively
`u`	flag to enable unicode matching
`p{}`	Unicode character sets
`P{}`	negated unicode character sets
see MDN: Unicode property escapes for details
`u{}`	specify unicode characters using codepoints

Lookarounds	Description
lookarounds	allows to create custom positive/negative assertions
zero-width like anchors and not part of matching portions
`(?!pat)`	negative lookahead assertion
`(?<!pat)`	negative lookbehind assertion
`(?=pat)`	positive lookahead assertion
`(?<=pat)`	positive lookbehind assertion
variable length lookbehind is allowed
`(?!pat1)(?=pat2)`	multiple assertions can be specified next to each other in any order
as they mark a matching location without consuming characters
`((?!pat).)*`	Negates a regexp pattern

Matched portion	Description
`m = s.match(/pat/)`	assuming `g` flag isn't used and regexp succeeds,
returns an array with matched portion and 3 properties
`index` property gives the starting location of the match
`input` property gives the input string `s`
`groups` property gives dictionary of named capture groups
`m[0]`	for above case, gives entire matched portion
`m[N]`	matched portion of Nth capture group
`s.match(/pat/g)`	returns only the matched portions, no properties
`s.matchAll(/pat/g)`	returns an iterator containing details for
each matched portion and its properties
Backreference	gives matched portion of Nth capture group
use `$1`, `$2`, `$3`, etc in replacement section
`$&` gives entire matched portion
$` gives string before the matched portion
`$'` gives string after the matched portion
use `1`, `2`, `3`, etc within regexp definition
`$$`	insert `$` literally in replacement section
`$0N`	same as `$N`, allows to separate backreference and other digits
`Nxhh`	allows to separate backreference and digits in regexp definition
`(?<name>pat)`	named capture group
use `k<name>` for backreferencing in regexp definition
use `$<name>` for backreferencing in replacement section

Regular expression examples🔗

test method

new RegExp() constructor

string and line anchors

replace method and word boundaries

Javascript Cheat Sheet Github Download

alternations and grouping

MDN: Regular Expressions doc provides escapeRegExp function, useful to automatically escape metacharacters.
- See also XRegExp utility which provides XRegExp.escape and XRegExp.union methods. The union method has additional functionality of allowing a mix of string and RegExp literals and also takes care of renumbering backreferences.

dot metacharacter and quantifiers

match method

matchAll method

function/dictionary in replacement section

split method

backreferencing with normal/non-capturing/named capture groups

Github Search Cheat Sheet

examples for lookarounds

Javascript Cheat Sheet Github

Debugging and Visualization tools🔗

As your regexp gets complicated, it can get difficult to debug if you run into issues. Building your regexp step by step from scratch and testing against input strings will go a long way in correcting the problem. To aid in such a process, you could use various online regexp tools.

Github Cheat Sheet Pdf

regex101 is a popular site to test your regexp. You'll have first choose the flavor as JavaScript. Then you can add your regexp, input strings, choose flags and an optional replacement string. Matching portions will be highlighted and explanation is offered in separate panes. There's also a quick reference and other features like sharing, code generator, quiz, etc.

Another useful tool is jex: regulex which converts your regexp to a rail road diagram, thus providing a visual aid to understanding the pattern.

Javascript Cheat Sheet Github Example

JavaScript RegExp book🔗

Visit my repo learn_js_regexp for details about the book I wrote on JavaScript regular expressions. The ebook uses plenty of examples to explain the concepts from the basics and includes exercises to test your understanding. The cheatsheet and examples presented in this post are based on contents of this book.