From 0a9648c392f2b1eb57b3fc1cf82345f4443518a1 Mon Sep 17 00:00:00 2001
From: Jerko Steiner <jerko.steiner@gmail.com>
Date: Tue, 2 Apr 2019 14:38:01 +0800
Subject: [PATCH] Add packages/common/src/types.ts

---
 packages/common/src/index.ts |  1 +
 packages/common/src/types.ts | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 packages/common/src/types.ts

diff --git a/packages/common/src/index.ts b/packages/common/src/index.ts
index 60d69e1..c8387be 100644
--- a/packages/common/src/index.ts
+++ b/packages/common/src/index.ts
@@ -12,4 +12,5 @@ export * from './IUserTeam'
 export * from './ReadonlyRecord'
 export * from './URLFormatter'
 export * from './indexBy'
+export * from './types'
 export * from './without'
diff --git a/packages/common/src/types.ts b/packages/common/src/types.ts
new file mode 100644
index 0000000..e9f225c
--- /dev/null
+++ b/packages/common/src/types.ts
@@ -0,0 +1,22 @@
+/**
+ * transform unknown into undefined
+ */
+export type Optional<T> = T extends {} ? T : undefined
+
+export type NonUndefinedPropertyNames<T> = {
+  [K in keyof T]: T[K] extends undefined ? never: K
+}[keyof T]
+
+export type OnlyRequired<T> = Pick<T, NonUndefinedPropertyNames<T>>
+
+export type NonUnknownPropertyNames<T> = {
+  [K in keyof T]: T[K] extends {} ? K : never
+}[keyof T]
+
+export type OnlyDefined<T> = Pick<T, NonUnknownPropertyNames<T>>
+
+/**
+ * Remove types from T that are not assignable to U
+ * https://www.typescriptlang.org/docs/handbook/advanced-types.html
+ */
+export type Filter<T, U> = T extends U ? T : never