Initial commit

global.d.ts

@@ -0,0 +1,36 @@
+interface String {
+  startsWith<S extends string>(searchString: S): this is `${S}${string}`;
+  endsWith<S extends string>(searchString: S): this is `${string}${S}`;
+  includes<S extends string>(
+    searchString: S,
+    position?: number,
+  ): this is `${string}${S}${string}`;
+}
+
+type LiteralUnionLike<T> = T extends string
+  ? T extends ""
+    ? T
+    : T extends `${T}${T}`
+      ? never
+      : T
+  : T extends number
+    ? `${T}0` extends `${number}`
+      ? T
+      : never
+    : T extends null | undefined
+      ? T
+      : never;
+
+interface Array<T> {
+  includes(
+    searchElement: T extends LiteralUnionLike<T> ? unknown : never,
+    fromIndex?: number,
+  ): searchElement is T extends LiteralUnionLike<T> ? T : never;
+}
+
+interface ReadonlyArray<T> {
+  includes(
+    searchElement: T extends LiteralUnionLike<T> ? unknown : never,
+    fromIndex?: number,
+  ): searchElement is T extends LiteralUnionLike<T> ? T : never;
+}