TypeScriptTips

Make bugs impossible.
One TypeScript tip at a time.

I like the tricks :) – Kasia

Prefer static types over tests

@RiccardoOdone•Suggest a tip•

Static types are automated tests that run continuously (and prevent the wrong types from propagating through your program).

const doA = (): any => {}
const doB = (x: any): any => {}
const doC = (x: any): any => {}

const go = (condition: any): any => {
  const x = doA()
  return condition ? doB(x) : doC(x)
}
// ⛔️ What if doA() changes the return type?
// ⛔️ What if doB() changes the input type?
// ⛔️ What if doC() changes the input type?
// ⛔️ Are doB() and doC() returning the same type?
// ⛔️ Do doB() and doC() work with any x?
// ⛔️ What if condition is 0, '', NaN, null, undefined?

const doA = (): T => {}
const doB = (x: T): R => {}
const doC = (x: T): R => {}

const go = (condition: boolean): R => {
  const x = doA()
  return condition ? doB(x) : doC(x)
}
// Does not compile if:
// ✅ doA() changes the return type
// ✅ doB() changes the input type
// ✅ doC() changes the input type
// ✅ doB() and doC() stop returning the same type
// ✅ doB() and doC() are not passed a T
// ✅ condition is 0, '', NaN, null, undefined
Type-safe carouselDo not throwFilter using a type assertionUse precise typesType-safe string templatingEnumerating a union typeNumbers with unitsZero nullEnumerating statusesAnd typesAvoiding window as anyUse descriptive valuesCheck authorization with typesExtract union types from record typesKeep in sync with conditional typesType-safe pickPass arguments by namePick instead of duplicatingPrevent mutationsType aliasesModel with different typesPrefer static types over testsPush conditionals downType-level functionsCheck Authorization With Types (again)From Union to TupleLimit typesLaser-focused typesCallable typesPartial considered harmfulSatisfy typesWTH?!Parse, don't castNarrow typesFetch footgunModel with different types (2)Polymorphic typesParse, don't cast (again)Type-safe envObject vs Recordconst Type ParametersDigType checksExpand intellisenseNumbers with units (2)Unchecked indexed accessExtract instead of duplicating

TypeScriptTips

Crafted with 💛 by Riccardo