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The following breaking changes occurred between the release of TypeScript 3.9 and the release of TypeScript 4.7:

TypeScript 4.0

• Attempts to override a parent class's accessor with a property declaration now yield an error (4.0).
• If you enable the --strictNullChecks compiler flag, you have to provide optional arguments for delete operators (4.0)

TypeScript 4.1

• Users cannot mark abstract members as async (4.1).
• The resolve() function in a Promise must return a value (4.1).
• When you enable the --strictNullChecks compiler flag, && expre