In this episode of Syntax, Scott and Wes continue their discussion of TypeScript Fundamentals with a deeper diver into more advanced use cases. Deque - Sponsor Deque’s axe DevTools makes accessibility testing easy and doesn’t require special expertise. Find and fix issues while you code. Get started with a free trial of axe DevTools Pro at deque.com/syntax. No credit card needed. LogRocket - Sponsor LogRocket lets you replay what users do on your site, helping you reproduce bugs and fix issues faster. It’s an exception tracker, a session re-player and a performance monitor. Get 14 days free at logrocket.com/syntax. Mux - Sponsor Mux Video is an API-first platform that makes it easy for any developer to build beautiful video. Powered by data and designed by video experts, your video will work perfectly on every device, every time. Mux Video handles storage, encoding, and delivery so you can focus on building your product. Live streaming is just as easy and Mux will scale with you as you grow, whether you’re serving a few dozen streams or a few million. Visit mux.com/syntax. Show Notes Deep end stuff 03:30 - any vs unknown 06:20 - never https://twitter.com/Igorbdsq/status/1351681019196436482 09:14 - .d.ts Definition files Usually for existing libraries that don’t have types Can be generated or hand-written Also really handy for pure JS projects, you still get good autocomplete because of these 13:25 - Type generation Can be generated from GraphQL, or Schemas, or from JSON Output 17:20 - TypeScript generics (variables) Kind of like functions, they return something different based on what you pass it makeFood makeFood This function makes food and shares lots of the same functionality between making a pizza and sandwich If the only thing that differs is the type returned, we can use generics You often see this as a single char T It can be anything Promise is a generic querySelector uses generics 21:48 - Promises / Async + Await Functions now return a Promise type, but with a generic Promise Promise Promise, Request, Request stringified added headers 29:48 - Type assertion (type casting) Type assertion is when you want to tell TypeScript “Hey I know better than you”. Two ways: as keyword (most popular) someValue as HTMLParagraphElement Tagged before someValue 34:14 - TypeScript without TypeScript (JSDoc / TSDoc) Really nice! You can also add comments / descriptions https://github.com/developit/redaxios/blob/master/src/index.js 40:08 - Interfaces vs Types Interfaces have better perf https://twitter.com/wesbos/status/1362418379919937545 https://blog.logrocket.com/types-vs-interfaces-in-typescript/ What do you default to? How we write TypeScript 44:27 - Interface or Types Scott - Types Wes - Interfaces 44:50 - any vs unknown Scott - any Wes - unknown / any 46:52 - Any (No Implicit or Implicit Allowed) Scott - No implicit any Wes - No implicit any 48:31 - Return types (Implicit or Explicit) Scott - Explicit always Wes - Not always 50:49 - Compile (TSC, Strip TS) Scott - Strip Wes - Both 52:38 - Type Assertion (as or ) Scott - as Wes - as 53:09 - Arrays (Dog[] or Array) Scott - Dog[] Wes - Dog[] 54:02 - Assert or Generic (if both work) querySelector(’.thing’) as HTMLVideoElement; or querySelector(’.thing’); Scott - querySelector(’.thing’); Wes - querySelector(’.thing’); Links Syntax 324: TypeScript Fundamentals Syntax 327: Hasty Treat - TypeScript Compilers and Build Tools Axios VS Code Syntax 310: Serverless, Deno and TypeScript with Brian Leroux Cloudinary Notion ××× SIIIIICK ××× PIIIICKS ××× Scott: Powerowl 16 Battery Recharger Wes: Fairywill Pro P11 Shameless Plugs Scott: Level 2 Node Authentication - Sign up for the year and save 25%! Wes: Beginner Javascript - Use the coupon code ‘Syntax’ for $10 off! Tweet us your tasty treats! Scott’s Instagram LevelUpTutorials Instagram Wes’ Instagram Wes’ Twitter Wes’ Facebook Scott’s Twitter Make sure to include @SyntaxFM in your tweets