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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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’);

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TypeScript Fundamentals — Getting a Bit Deeper

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