TypeScript Fundamentals — Getting a Bit Deeper

In this episode of Syntax, Scott and Wes continue their discussion of TypeScript Fundamentals with a deeper diver into more advanced use cases.

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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?

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’);

• 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

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• Wes: Fairywill Pro P11

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