feat(types): add Join

src/index.ts

@@ -14,6 +14,7 @@ export type { DeepRequired } from './types/DeepRequired'
 export type { EmptyValue } from './types/EmptyValue'
 export type { FIXME } from './types/FIXME'
 export type { IndexSignature } from './types/IndexSignature'
+export type { Join } from './types/Join'
 export type {
   JSONArray,
   JSONObject,

src/types/Join.ts

@@ -0,0 +1,19 @@
+import type { IndexSignature } from './IndexSignature'
+
+/**
+ * @file Types - Join
+ * @module types/Join
+ */
+
+/**
+ * Constructs a string array by concatenating string `S` and `S1`.
+ *
+ * @template S - String to split
+ * @template S2 - String delimiter
+ * @template D - String delimiter
+ */
+export type Join<
+  S extends IndexSignature,
+  S1 extends IndexSignature,
+  D extends string = ''
+> = `${S & string}${D}${S1 & string}`