refactor: split files

src/capitalize.ts

@@ -0,0 +1,14 @@
+import { charAt } from './charAt.js'
+import { join } from './join.js'
+import { slice } from './slice.js'
+import { toUpperCase } from './toUpperCase.js'
+
+/**
+ * Capitalizes the first letter of a string. This is a runtime counterpart of `Capitalize<T>` from `src/types.d.ts`.
+ * @param str the string to capitalize.
+ * @returns the capitalized string.
+ * @example capitalize('hello world') // 'Hello world'
+ */
+export function capitalize<T extends string>(str: T): Capitalize<T> {
+  return join([toUpperCase(charAt(str, 0)), slice(str, 1)])
+}