JavaScript Native Contracts

• Callable — Any value that can be invoked with () operator
• Function — Callable object, with optional this binding or arrow
• AsyncFunction — Promise-returning Function
• Callback — A function passed to another function to be called later
• Callback-last-error-first — Callback contract or convention (error, result) signature, where error is Error | null, and result is returned if no error
• Thenable — Any object with a .then(fn) method
• Promise — Thenable with then, catch, and finally
• Iterable — Has [Symbol.iterator]() that returns an Iterator
• AsyncIterable — Has [Symbol.asyncIterator]() that returns an AsyncIterator
• Iterator — Has .next() returning { value, done } structure
• Generator — A function producing an Iterator (sync or async), supporting next(), throw(), return()
• Array-like — Object with indexed keys 0, 1, ... and numeric .length, but no array methods
• Observable — Push-based data sours available for subscription
• EventTarget — DOM standard interface with .addEventListener(event, handler)
• EventEmitter — Node.js style event emitter with .on(event, handler) and .emit(event, ...args)
• Stream — Abstraction for flow (readable/writable/duplex) with backpressure support