JavaScript ES2024

Methods on the built-in objects, each with a live demo that runs the real thing in your browser. No console, no scratch file.

144 methods136 live demos
Sections
Methods LIVE
Array, String, Object, Number, Map, Set, Promise, Date and the globals.
144 entries →
Operators SOON
Spread, optional chaining, nullish coalescing, equality.
planned
Errors & exceptions SOON
TypeError, RangeError, and what actually throws them.
planned
Web APIs LATER
fetch, URL, Intl, and the browser globals devs reach for.
planned
Browse by type
Jump straight to the methods for a specific built-in object.
array38date11global8map7number11object20promise10set9string30
Featured — try the live demos
01Array.prototype.mapLIVE02Array.prototype.filterLIVE03Array.prototype.reduceLIVE04Array.prototype.sortLIVE05Array.prototype.sliceLIVE06Array.prototype.spliceLIVE
Python
Python reference →
Every built-in function and type method, with live in-browser demos verified against CPython.
Tools
JSON, Base64, JWT, and more →
Client-side developer utilities — formatters, encoders, minifiers. Everything runs in your browser.