ECMAScript

TypeScript does not allow developers to import modules with explicit .ts extensions, unlike standard ECMAScript/JavaScript practices. This forces module resolution traversal which is particularly slow over networks, and contradicts TypeScript's own design where the team knows .ts files must be transpiled to .js anyway.

JavaScript's long history creates technical debt through legacy patterns, older syntax, and poorly maintained libraries that still exist in many codebases. Backward compatibility requirements slow innovation, forcing the language to straddle old and new idioms simultaneously.

TypeScript's long-term viability depends on TC39's type-annotations proposal, which faces significant consensus issues within the committee itself. The proposal would only treat annotations as comments with no enforcement, leaving TypeScript's theoretical future as a superset uncertain.