Top 1K Features Creators Events Podcasts Books Extensions Interviews Blog Explorer CSV

JavaScript

< >
LEET SHEET terminal edit

JavaScript is an open source programming language created in 1995 by Brendan Eich.

#1on PLDB 29Years Old 16mRepos
Leet Sheet · REPL · Spec · Wikipedia · Subreddit · Docs

JavaScript (), often abbreviated as JS, is a high-level, dynamic, weakly typed, prototype-based, multi-paradigm, and interpreted programming language. Alongside HTML and CSS, JavaScript is one of the three core technologies of World Wide Web content production. It is used to make webpages interactive and provide online programs, including video games. Read more on Wikipedia...


Example from Riju:
console.log("Hello, world!");
Example from hello-world:
console.log("Hello World");
Example from the Hello World Collection:
// Hello world in JavaScript console.log("Hello World");
Example from Linguist:
alert("dude!")
Example from Wikipedia:
var minstake = 0.00000100; // valor base //----------------------------------------- var autorounds = 99; // n° de rolls //====================================================== // if (profit > profit_max) { // error_title = "Maximum profit exceeded"; // error_info = "Maximum profit: " + number_format(profit_max, devise_decimal); // error_value = "Maximum profit exceeded - Maximum profit: " + number_format(profit_max, devise_decimal); // error = true; // } // else if (amount > balance) { // error_title = "Bet amount"; // error_info = "Maximum bet: " + number_format(balance, devise_decimal); // error_value = "Bet amount - Maximum bet: " + number_format(balance, devise_decimal); // error = true; // } var handbrake = 1.0000000; // valor lose pause game var autoruns = 1; // else if (amount > bet_max) { // error_title = "Bet amount"; // error_info = "Maximum bet: " + number_format(bet_max, devise_decimal); // error_value = "Bet amount - Maximum bet: " + number_format(bet_max, devise_decimal); // error = true; // } // else if (amount < bet_min) { // error_title = "Bet amount"; // error_info = "Minimum bet: " + number_format(bet_min, devise_decimal); // error_value = "Bet amount - Minimum bet: " + number_format(bet_min, devise_decimal); // error = true; // } function playnow() { if (autoruns > autorounds ) { console.log('Limit reached'); return; } document.getElementById('double_your_btc_bet_hi_button').click(); setTimeout(checkresults, 1000); return;} function checkresults() { if (document.getElementById('double_your_btc_bet_hi_button').disabled === true) { setTimeout(checkresults, 1000); return; } var stake = document.getElementById('double_your_btc_stake').value * 1; var won = document.getElementById('double_your_btc_bet_win').innerHTML; if (won.match(/(\d+\.\d+)/) !== null) { won = won.match(/(\d+\.\d+)/)[0]; } else { won = false; } var lost = document.getElementById('double_your_btc_bet_lose').innerHTML; if (lost.match(/(\d+\.\d+)/) !== null) { lost = lost.match(/(\d+\.\d+)/)[0]; } else { lost = false; } if (won && !lost) { stake = minstake; console.log('Bet #' + autoruns + '/' + autorounds + ': Won ' + won + ' Stake: ' + stake.toFixed(8)); } if (lost && !won) { stake = lost * 2.1; console.log('Bet #' + autoruns + '/' + autorounds + ': Lost ' + lost + ' Stake: ' + stake.toFixed(8)); } if (!won && !lost) { console.log('Something went wrong'); return; } document.getElementById('double_your_btc_stake').value = stake.toFixed(8); autoruns++; if (stake >= handbrake) { document.getElementById('handbrakealert').play(); console.log('Handbrake triggered! Execute playnow() to override'); return; } setTimeout(playnow, 1000); return; }playnow()
Fun fact:
The name Java in JavaScript was pure marketing: "At the time, the dot-com boom had begun and Java was the hot new language, so Eich considered the JavaScript name a marketing ploy by Netscape"
JavaScript Keywords
abstract arguments await boolean break byte case catch char class const continue debugger default delete do double else enum eval export extends false final finally float for function goto if implements import in instanceof int interface let long native new null package private protected public return short static super switch synchronized this throw throws transient true try typeof var void volatile while with yield

Language features

Feature Supported Example Token
Standard Library ✓ console.log("Hello, World!");
Scientific Notation ✓
Binary Literals ✓ // 0[bB][01]+n? 0b100110100000110011110010010
Floats ✓ // (\.[0-9]+|[0-9]+\.[0-9]*|[0-9]+)([eE][-+]?[0-9]+)? 80766866.0
Hexadecimals ✓ // 0[xX][0-9a-fA-F]+n? 0x4D06792
Octals ✓ // 0[oO]?[0-7]+n? 0o464063622
Sets ✓ set = new Set() set.add("foo")
Function Composition ✓ function o(f, g) { return function(x) { return f(g(x)); } }
Destructuring ✓ const o = {p: 42, q: true}; const {p, q} = o;
Default Parameters Pattern ✓ function multiply(a, b = 1) { return a * b; }
Line Comments ✓ // A comment //
Increment and decrement operators ✓ let i = 0 i++ i--
Methods ✓ class Person { method1() {} method2() {} }
Functions ✓ function helloWorld() {console.log("hi")}
Case Sensitivity ✓
Zero-based numbering ✓
While Loops ✓ let times = 10 while (times) {times--} console.log("done")
Ternary operators ✓ let i = true ? 1 : 0
Switch Statements ✓ var animal = "dog" switch (animal) { case "dog": console.log("yay"); break; case "cat": console.log("oh"); break; }
Strings ✓ "hello world" `
Letter-first Identifiers ✓
Inheritance ✓ class B {} class A extends B {}
Print() Debugging ✓ console.log("Hi") console.log
References ✓
Operators ✓ 1 + 1
Multiline Strings ✓ const lines = `one two`
Anonymous Functions ✓ (() => console.log("hello world"))()
Infix Notation ✓ const six = 2 + 2 + 2
Implicit Type Casting ✓ console.log("hello " + 2)
Assignment ✓ var name = "John" =
Directives ✓ "use strict"; "use asm";
Generators ✓ function* fibonacci(limit) { let [prev, curr] = [0, 1]; while (!limit || curr <= limit) { yield curr; [prev, curr] = [curr, prev + curr]; } } // bounded by upper limit 10 for (let n of fibonacci(10)) { console.log(n); } // generator without an upper bound limit for (let n of fibonacci()) { console.log(n); if (n > 10000) break; } // manually iterating let fibGen = fibonacci(); console.log(fibGen.next().value); // 1 console.log(fibGen.next().value); // 1 console.log(fibGen.next().value); // 2 console.log(fibGen.next().value); // 3 console.log(fibGen.next().value); // 5 console.log(fibGen.next().value); // 8 // picks up from where you stopped for (let n of fibGen) { console.log(n); if (n > 10000) break; }
Garbage Collection ✓
First-Class Functions ✓ [2.0,1.1].map(Math.round)
Exceptions ✓ try { undefinedFn() } catch (err) { console.log(err) }
Dynamic Typing ✓
Constants ✓ const one = 1
Constructors ✓ class Person { constructor(name) { this._name = name } } new Person("Jane")
Labels ✓ main: console.log("pldb")
Comments ✓ // A comment
Conditionals ✓ if (true) console.log("hi!")
Classes ✓ class Person {}
Method Chaining ✓ "hello world".toString().substr(0, 1).length
Booleans ✓ true false
Magic Getters and Setters ✓ // Can be implemented in ES6 using proxies: "use strict"; if (typeof Proxy == "undefined") { throw new Error("This browser doesn't support Proxy"); } let original = { "foo": "bar" }; let proxy = new Proxy(original, { get(target, name, receiver) { let rv = Reflect.get(target, name, receiver); if (typeof rv === "string") { rv = rv.toUpperCase(); } return rv; } }); console.log(`original.foo = ${original.foo}`); // "original.foo = bar" console.log(`proxy.foo = ${proxy.foo}`); // "proxy.foo = BAR"
Dynamic Properties ✓ class Person {} const person = new Person() person.age = 50
Source Maps ✓ { version: 3, file: 'min.js', names: ['bar', 'baz', 'n'], sources: ['one.js', 'two.js'], sourceRoot: 'http://example.com/www/js/', mappings: 'CAAC,IAAI,IAAM,SAAUA,GAClB,OAAOC,IAAID;CCDb,IAAI,IAAM,SAAUE,GAClB,OAAOA' };
Bitwise Operators ✓ var x = 5 & 1;
Single Dispatch ✓
Polymorphism ✓ "a" + "b"; 1 + 2
MultiLine Comments ✓ /* A comment */ /* */
Merges Whitespace ✓
Lists ✓ const list = [1,2,3]
Integers ✓ 80766866
Breakpoints ✓ if (false) debugger
Partial Application ✓ const addNumbers = (num1, num2) => num1 + num2 const add5 = num => addNumbers(10, num)
Map Functions ✓ [1,2.1].map(Math.round)
Binary Operators ✓ 1 + 1
Async Await ✓ async doSomething => await somethingElse()
Expressions ✓ 1 + 1
Regular Expression Syntax Sugar ✓ console.log("Hello World".match(/\w/))
Statements ✓ let x = 3;
File Imports ✓ import { helloWorld } from "./helloWorld.js";
hasExports ✓ export function myFunction() { }
hasSymbols ✓ // A symbol is a unique and immutable primitive value, often used as a unique key for object properties pldb = Symbol()
Operator Overloading X
Case Insensitive Identifiers X
Multiple Inheritance X
Function Overloading X
Macros X
Processor Registers X
Multiple Dispatch X
Pointers X
Semantic Indentation X
Abstract Types X
Access Modifiers X
Variable Substitution Syntax X
Enums X
S-Expressions X

- Build the next great programming language · Add · Issues · About · Search · Keywords · Livestreams · Labs · Resources · Acknowledgements

Built with Scroll v154.3.0