Add discriminate helper

Author: skovhus

server/src/util/discriminate.ts

@@ -0,0 +1,8 @@
+export function discriminate<K extends PropertyKey, V extends string | number | boolean>(
+  discriminantKey: K,
+  discriminantValue: V,
+) {
+  return <T extends Record<K, any>>(
+    obj: T & Record<K, V extends T[K] ? T[K] : V>,
+  ): obj is Extract<T, Record<K, V>> => obj[discriminantKey] === discriminantValue
+}