This is a collection of questions that come up every now and then about syntax in JavaScript. This is also a Community Wiki, so everyone is invited to participate in maintaining this list.
Stack Overflow does not allow searching for particular characters. As a consequence, many questions about operators and other syntax tokens are not found easily when searching for them. This also makes closing duplicates more difficult. The list below is to help with this issue.
The main idea is to have links to existing questions on Stack Overflow, so it's easier for us to reference them, not to copy over content from the ECMAScript Spec.
Additionally, this is a blatant copy of the PHP symbol reference. We needed a JS one.
Please help. Edit and add links to other operators/syntax references, or if you can't find good questions/answers on a particular piece of syntax, add an answer to this question and link it
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See the documentation on MDN about expressions and operators and statements.
this keyword:var x = function() vs. function x() — Function declaration syntax(function(){…})() — IIFE (Immediately Invoked Function Expression)(function(){…})(); work but function(){…}(); doesn't?(function(){…})(); vs (function(){…}());!function(){…}(); - What does the exclamation mark do before the function?+function(){…}(); - JavaScript plus sign in front of function expression! vs leading semicolon(function(window, undefined){…}(window));someFunction()() — Functions which return other functions=> — Equal sign, greater than: arrow function expression syntax|> — Pipe, greater than: Pipeline operatorfunction*, yield, yield* — Star after function or yield: generator functions[], Array() — Square brackets: array notationIf the square brackets appear on the left side of an assignment ([a] = ...), or inside a function's parameters, it's a destructuring assignment.
{key: value} — Curly brackets: object literal syntax (not to be confused with blocks)If the curly brackets appear on the left side of an assignment ({ a } = ...) or inside a function's parameters, it's a destructuring assignment.
`…${…}…` — Backticks, dollar sign with curly brackets: template literals`…${…}…` code from the node docs mean?/…/ — Slashes: regular expression literals$ — Dollar sign in regex replace patterns: $$, $&, $`, $', $n() — Parentheses: grouping operatorobj.prop, obj[prop], obj["prop"] — Square brackets or dot: property accessors?., ?.[], ?.() — Question mark, dot: optional chaining operator:: — Double colon: bind operatornew operator...iter — Three dots: spread syntax; rest parameters(...args) => {} — What is the meaning of “…args” (three dots) in a function definition?[...iter] — javascript es6 array feature […data, 0] “spread operator”{...props} — Javascript Property with three dots (…)++, -- — Double plus or minus: pre- / post-increment / -decrement operatorsdelete operatorvoid operator+, - — Plus and minus: addition or concatenation, and subtraction operators; unary sign operators|, &, ^, ~ — Single pipe, ampersand, circumflex, tilde: bitwise OR, AND, XOR, & NOT operators~1 equal -2?% — Percent sign: remainder operator&&, ||, ! — Double ampersand, double pipe, exclamation point: logical operators?? — Double question mark: nullish-coalescing operator** — Double star: power operator (exponentiation)x ** 2 is equivalent to Math.pow(x, 2)==, === — Equal signs: equality operators!=, !== — Exclamation point and equal signs: inequality operators<<, >>, >>> — Two or three angle brackets: bit shift operators?…:… — Question mark and colon: conditional (ternary) operator= — Equal sign: assignment operator%= — Percent equals: remainder assignment+= — Plus equals: addition assignment operator&&=, ||=, ??= — Double ampersand, pipe, or question mark, followed by equal sign: logical assignments||= (or equals) in JavaScript?, — Comma operator{…} — Curly brackets: blocks (not to be confused with object literal syntax)var, let, const — Declaring variableslabel: — Colon: labels# — Hash (number sign): Private methods or private fieldsSource: Stackoverflow.com