DefinedValue

DefinedValue = { } | null

Defined in: packages/core/src/types/defined-value.ts:19

Constraint for a type parameter that must never include undefined.

undefined is the absence of a value, not a value. An API that returns T | undefined to mean “there is nothing here” cannot also carry undefined as an element, because the two would be indistinguishable. Use null for a value that means nothing.

{} | null is every type except undefined and void.

Example:

class Queue<T extends DefinedValue> {
  dequeue(): T | undefined; // undefined can only mean "empty"
}