Cannot find module '@angular-devkit/build-webpack' code example
Example 1: An unhandled exception occurred: Cannot find module '@angular-devkit/build-angular/package.json' Require stack:
npm install --save-dev @angular-devkit/build-angular
Example 2: Could not find module "@angular-devkit/build-angular
ng update @angular/cli @angular/core
If you are updating from angular 7 to angular 8 then do this
ng update @angular/cli @angular/core
for more information read here https://github.com/just-jeb/angular-builders/blob/master/MIGRATION.MD