BREAKING_CHANGES.md

Angular 7.x

When upgrading from v6 and lower, you must change the module format from es2015 to commonjs in all your tsconfig files.

Before

{
    "compilerOptions":{
        "module": "es2015"
    }
}

After

{
    "compilerOptions":{
        "module": "commonjs" // if it's already commonjs, you're ok
    }
}