TypeScript Recipes vs JS Quiz

Tap Run and the real output appears right under the code, along with any type errors. You know what the code does before it goes into your project. No Node.js or TypeScript to install, no IDE, no account. 360+ short examples, one task each. Over 90% run on Node.js 24 and pass strict TypeScript 7 type checking. You know what you need, but not the exact syntax: • How do I remove duplicates from an array? • How do I get an enum value from its name? • How do I merge two Maps? Each has a working example here. • 22 sections, including strings and dates, arrays and collections, classes and interfaces, enums, generics, arrow functions, async/await, exception handling, regular expressions, files, JSON, algorithms, and design patterns. • What changed from TypeScript 3.0 to 5.5, with before-and-after code: the unknown type, the ?. and ?? operators, template literal types, the satisfies operator, using declarations. • Reference, 120+ entries: keywords, operators, and utility types such as Partial, Pick, Record, and ReturnType. Tap a word in the code to look it up. • 200+ SQL queries: JOIN, GROUP BY, subqueries, window functions; more than half run on a practice database. • Search looks inside the code: type reduce to find every example that uses it. • Edit an example and run your version, or write your own: a type error shows up right away. • Works on iPhone, iPad, and Mac. • Everything except running code works offline. Free version: 190+ TypeScript examples and 120+ SQL queries, the full reference, and 12 runs and 12 edits a day (TypeScript and SQL runs share one limit). Full version: all examples and queries, unlimited edits and examples of your own, and up to 30 TypeScript and 80 SQL runs a day. One-time purchase, no subscription. Built by a developer for developers. The project behind it has been in active development since 2015.

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