add optional utility type

types/Optional.ts

@@ -0,0 +1,18 @@
+/**
+ * Makes some properties of a record optional.
+ */
+export type Optional<T, K extends keyof Record<PropertyKey, unknown>> = Omit<T, K> & { [K in keyof T]?: T[K] }
+
+/*
+ * Example:
+ *   type CartItem = {
+ *     id: string,
+ *     sku: string,
+ *     quantity: number,
+ *   }
+ *
+ *   function addItem(item: Optional<CartItem, 'id' | 'quantity'>) {
+ *     // typeof item: { id?: string, sku: string, quantity?: number }
+ *     ...
+ *   }
+ */

types/index.ts

@@ -1,2 +1,3 @@
 export * from './Branded.ts'
 export * from './DeepPartial.ts'
+export * from './Optional.ts'