🐞 Bug report

Command

• serve

Is this a regression?

No, I've seen it in older version of Angular CLI.

Description

After updating TypeScript version to the one that is not supported by Angular Compiler, there is an error that is being thrown in terminal after running ng serve, but the dev server is not terminated, thus leading to some confusion on whether the error is actually fatal or not. Trying to access the webpage (root/index one) results in a error as well (Cannot GET /).

🔬 Minimal Reproduction

1. Create an app using ng new
2. Change the version of the "typescript" package to the one outside of the supported range (like 4.0.0-beta) in package.json
3. Run ng serve

🔥 Exception or Error

ERROR in The Angular Compiler requires TypeScript >=3.9.2 and <4.0.0 but 4.0.0-beta was found instead.
** Angular Live Development Server is listening on localhost:4200, open your browser on http://localhost:4200/ **

🌍 Your Environment

Angular CLI: 9.1.8
Node: 13.3.0
OS: darwin x64

Angular: 10.0.5
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router
Ivy Workspace: Yes

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.1000.4
@angular-devkit/build-angular     0.1000.4
@angular-devkit/build-optimizer   0.1000.4
@angular-devkit/build-webpack     0.1000.4
@angular-devkit/core              10.0.4
@angular-devkit/schematics        10.0.4
@angular/cli                      10.0.4
@ngtools/webpack                  10.0.4
@schematics/angular               10.0.4
@schematics/update                0.1000.4
rxjs                              6.5.5
typescript                        4.0.0-beta
webpack                           4.43.0