Compiler and Language

• Less context-sensitivity on this-less functions
• More-precise checking under exactOptionalPropertyTypes
• Allow subpath imports starting with #/
• Allow --module commonjs and --moduleResolution bundler
• lib.d.ts updates for 6.0

Breaking Changes and Deprecations

See the broader discussion at 6.0 Deprecation Candidates

• Deprecate --target es5 and adjust lowest target to es2015
• Deprecate --outFile
• Deprecate support for baseUrl
• Deprecate --moduleResolution node10
• Deprecate --moduleResolution classic
• Deprecate support for using module in place of namespace
• Deprecate support for import assertions
• Deprecate support for /// <reference no-default-lib />
• Deprecate support for /// <amd-module name=... />
• Deprecate less-used --module targets (AMD/System/UMD)
• Deprecate --downlevelIteration

Defaults and Behavioral Changes

• Enable --strict by default
• Assume "use strict" everywhere by default
• Change default --target to latest ECMAScript
• Error when CLI options are used with tsconfig.json
• Default types to [] in tsconfig.json
• Assume rootDir is the config directory
• Enable --noUncheckedSideEffectImports by default
• Default libReplacement to false