Nullish values

⬅️ FEM TypeScript Fundamentals #✅

Nullish values

null

• null means: there is a value, and that value is nothing.

undefined

• undefined means the value isn’t available (yet?)

let notDefined: undefined = null;
notDefined;
 
// Result:
 
type error: Type 'null' is not assignable to type 'undefined'.

void

• void should exclusively be used to describe that a function’s return value should be ignored

Non-null assertion operator

• aka optional chaining, the non-null assertion operator (!) is used to cast away the possibility that a value might be null or undefined.

type GroceryCart = {
  fruits?: { name: string; qty: number }[]
  vegetables?: { name: string; qty: number }[]
}
 
const cart: GroceryCart = {}
 
cart.fruits.push({ name: "kumkuat", qty: 1 })
cart.fruits!.push({ name: "kumkuat", qty: 1 })

Definite assignment operator

• !:, same as above but used on class fields instead