TypeScript 6.0 launches strict mode by default and drops ES5 support

Short summary

TypeScript 6.0 enforces strict mode by default, removes ES5/ES3 targets entirely, and defaults to ESNext module resolution—affecting 70% of codebases. Teams must update tsconfig.json to handle stricter type checking, choose between ESM or Babel transpilation for legacy environments, and update CI/CD pipelines. This is intentional design to force ecosystem modernization.

• •Strict mode now mandatory; 70% of codebases that skipped it will face immediate CI failures
• •ES5/ES3 targets removed; legacy browser support requires Babel or equivalent transpilation
• •ESNext module resolution default; explicit CommonJS config required for Node CJS projects

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