Error: Can't resolve 'core-js/es7/reflect' in '\node_modules\@angular-devkit\build-angular\src\angular-cli-files\models

You should install [email protected] that contains this file/module. See preset-env docs.

If you'd like to use version 3.0, you can add the a path to your tsconfig.json file.

{
    "compilerOptions": {
        ...
        "paths": {
            "core-js/es7/reflect": [
                "node_modules/core-js/proposals/reflect-metadata"
            ]
        }
    }
}

Note: You need check the node_modules/core-js/proposals/reflect-metadata relative path and correct it if needed in your project structure.

For Angular 8 (source):

Angular CLI 8.0+ manages the required Angular polyfills directly and projects will not require a direct dependency on core-js (assuming an application does not manually include additional core-js polyfills).

I've resolved by:

• removing core-js from my package.json dependencies
• removing import 'core-js/es7/reflect'; from my test.ts

The version 3.0 of core-js has some breaking changes:

https://github.com/zloirock/core-js/blob/master/docs/2019-03-19-core-js-3-babel-and-a-look-into-the-future.md

You should find a line similar to this in one of your files: import "core-js/es7/reflect";

Change it to this: import "core-js/proposals/reflect-metadata";

In my case , i just changed -->

import 'core-js/es6/reflect';
import 'core-js/es7/reflect';

to

import 'core-js/es/reflect';

and it worked..