JavaScript code is already TypeScript code. Although it may have type errors, the compiler will still output a file (when it says 'error' it really means 'warning' unless the error occurred during parsing, which shouldn't be the case for JS that actually runs).
In terms of converting idiomatic JavaScript class/module-like structures into TypeScript classes or modules, there aren't any tools for that (yet). The TFS Team wrote an internal bespoke tool for their codebase to do this, but that was only really possible because their JS was written under very strict rules to begin with.