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The TypeScript compiler team deprecated const enums because they break isolated module compilation and cause runtime errors in modern build pipelines. Learn the technical reasons, migration strategies to union types and const objects, and why the deprecation protects codebases from silent failures.

Function overloads promise precise type inference, but first-match resolution and order dependency create maintainability traps. This guide shows when overloads clarify intent and when union types deliver better outcomes.

Master TypeScript's declaration merging to type globalThis properties without any. Learn when each pattern breaks, how module context affects global declarations, and better alternatives for most use cases.