feat: create js types

strings/js-string.ts

@@ -0,0 +1,35 @@
+export type Split<
+  T extends string,
+  F extends string = "",
+  $Draft extends readonly string[] = []
+> =
+  //
+  T extends `${infer $Value}${F}${infer $Rest}`
+    ? Split<$Rest, F, readonly [...$Draft, $Value]>
+    : F extends ""
+    ? $Draft
+    : readonly [...$Draft, T];
+
+export type Join<
+  T extends readonly (string | number)[],
+  F extends string = "",
+  $Draft extends string = ""
+> =
+  //
+  T["length"] extends 0
+    ? `${$Draft}`
+    : T extends [infer $First, ...infer $Rest]
+    ? $Rest extends (string | number)[]
+      ? $First extends string | number
+        ? Join<$Rest, F, $Draft extends "" ? $First : `${$Draft}${F}${$First}`>
+        : never
+      : never
+    : never;
+
+export type Length<T extends string> = Split<T>["length"];
+
+export type CharAt<
+  T extends string,
+  I extends keyof $StrArr,
+  $StrArr = Split<T>
+> = $StrArr[I];

strings/mod.ts

@@ -1 +1,2 @@
 export * from "./case/mod.ts";
+export * from "./js-string.ts";