TypeScript 4.1: New features and improvements

TypeScript 4.1, released in late November, introduces significant enhancements including template literal types, improved checking flags, and key remapping in mapped types, which allow developers to express types more precisely and flexibly. Notably, the update enables template literal string types, which use JavaScript-like syntax to create a union of possible string combinations, and introduces the noUncheckedIndexAccess flag to address potential undefined values in index signatures. The release also supports recursive conditional types, JSX factories for React 17, and simplifies Promise constructor arguments. These advancements aim to enhance the developer experience by offering more intuitive and powerful tools for type management and tracking in complex applications.