The ng upgrade command for updating cli version from a v7 project to v8 fails.
Manually trying to upgrade cli first also fails.
ng update @angular/cli
Your global Angular CLI version (8.0.1) is greater than your local version (7.3.9). The local Angular CLI version is used.
Package "@angular/compiler-cli" has an incompatible peer dependency to "typescript" (requires ">=3.1.1 <3.3", would install "3.4.5").
Incompatible peer dependencies found. See above.
try upgrading all packages using ng update --all --force if this doesn't work then try upgrading core and CLI ng update @angular/core @angular/cli.
and still not working then install typescript manually using npm i typescript@3.4
Like answer above, force the update, but in my case typescript@latest doesn't work because angular requires typescipt@3.4. If you force all it install 3.5 version and you must downgraded it
来源：https://stackoverflow.com/questions/56470993/ng-upgrade-command-fails-for-upgrading-cli-from-v7-to-v8