Syntax · JS Stuartsm

async / awaitSyntax for writing promise-based code that reads like ordinary sequential code — await pauses only the async function it's inside.
ClassesSyntax over the prototype mechanism — public and private fields, methods on the shared prototype, and extends for inheritance.
const and letThe two modern ways to declare a variable binding — const cannot be reassigned, let can.
Destructuring, Spread, and RestThree related bits of syntax built on ... and pattern-matching — pulling values out, copying/combining data, and gathering leftovers.
Equality Operators (=== and ==)Strict equality (===) never coerces types; loose equality (==) coerces one side according to a specific set of rules.
for await...of and Async GeneratorsIterates an async iterable — one whose Symbol.asyncIterator produces promises — the async counterpart to for...of.
for, while, and for...ofThree loop forms — for when counting or indexing, while when the iteration count isn't known up front, for...of when iterating a collection's values.
Function Declarations, Expressions, and Arrow FunctionsThree syntaxes for creating a function value, differing in hoisting behavior and how they handle this.
Generators and IteratorsThe Symbol.iterator protocol that powers for...of and spread, and generator functions (function*) as the easiest way to implement it.
HoistingHow each declaration type — var, function, let, const, class — is set up before line-by-line execution begins, and what's accessible before its own line runs.
if / else and switchBranching statements — if/else for arbitrary conditions, switch for one value compared against several exact matches.
import and exportModule syntax for sharing code between files — any number of named exports, at most one default export per module.
Optional Chaining (?.) and Nullish Coalescing (??)?. reads a property and stops safely if anything along the way is missing; ?? supplies a fallback only for null or undefined.
Statements and ExpressionsAn expression produces a value; a statement is a complete instruction that may contain one but isn't one itself.
Strict ModeAn opt-in restricted variant of JavaScript that turns several silent mistakes into thrown errors.
Symbols and Well-Known SymbolsA guaranteed-unique primitive type, used as a collision-free object key and to hook user objects into built-in language behavior via well-known symbols.
Template LiteralsBacktick-delimited strings that support embedded expressions and multi-line text without manual concatenation.
this, call, apply, and bindthis is determined by a function's call site, not where it's defined; call/apply/bind set it explicitly, and arrow functions have no this of their own.
try / catch / finallyRuns a block and, if it throws, catches the error instead of crashing the program; finally always runs afterward.