From e04a2d097d98cc4d33bf19f42291925dd79cc9ed Mon Sep 17 00:00:00 2001
From: Andrej Dyck <43913051+andrej-dyck@users.noreply.github.com>
Date: Sat, 16 Dec 2023 16:35:56 +0100
Subject: [PATCH] add nullable types functions

---
 index.ts           |  1 +
 nullables/index.ts | 11 +++++++++++
 2 files changed, 12 insertions(+)
 create mode 100644 nullables/index.ts

diff --git a/index.ts b/index.ts
index 624306a..0792fcf 100644
--- a/index.ts
+++ b/index.ts
@@ -1,5 +1,6 @@
 export * from './json/index.js'
 export * from './lazy/index.js'
 export * from './locale/index.js'
+export * from './nullables/index.js'
 export * from './raise/index.js'
 export * from './records/index.js'
diff --git a/nullables/index.ts b/nullables/index.ts
new file mode 100644
index 0000000..7d8c9fd
--- /dev/null
+++ b/nullables/index.ts
@@ -0,0 +1,11 @@
+/**
+ * Checks whenever a value is not nullable; same as value != null
+ *
+ * Useful for Array.filter():
+ *   const arr: (string | undefined)[] = [...]
+ *   ❌ arr.filter(v => v != null) // type: (string | undefined)[]
+ *   ❌ arr.filter(v => typeof v === 'string') // type: (string | undefined)[]
+ *   ✅ arr.filter(isNonNullable) // type: string[]
+ */
+export const isNonNullable = <T>(value: NonNullable<T> | undefined | null): value is NonNullable<T> =>
+  value != null