ng build throws downlevelIteration error targeting es2015

[lppedd]

🐞 Bug report

Command (mark with an x)

- [ ] new
- [x] build
- [ ] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] xi18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

Is this a regression?

Yes, the previous version in which this bug was not present was: 7.3.*

Description

Building with ng build while targeting es2015 throws downlevelIteration error.

🔬 Minimal Reproduction

Create a new Angular application and use this code for app.component.ts

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent implements OnInit {
  map = new Map<string, string>();

  ngOnInit(): void {
    this.map.set('key', 'value');

    for (const [k, v] of this.map) {
      console.log(k, v);
    }
  }
}

🔥 Exception or Error

ERROR in src/app/app.component.ts(15,26): error TS2569: Type 'Map' is not an array type or a string type. Use compiler option '--downlevelIteration' to allow iterating of iterators.

🌍 Your Environment

Angular CLI: 8.0.1
Node: 10.11.0
OS: win32 x64
Angular: 8.0.0
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.800.1
@angular-devkit/build-angular     0.800.1
@angular-devkit/build-optimizer   0.800.1
@angular-devkit/build-webpack     0.800.1
@angular-devkit/core              8.0.1
@angular-devkit/schematics        8.0.1
@angular/cli                      8.0.1
@ngtools/webpack                  8.0.1
@schematics/angular               8.0.1
@schematics/update                0.800.1
rxjs                              6.4.0
typescript                        3.4.5
webpack                           4.30.0

tsconfig.json

{
  "compileOnSave": false,
  "compilerOptions": {
    "baseUrl": "./",
    "outDir": "./dist/out-tsc",
    "sourceMap": true,
    "declaration": false,
    "module": "esnext",
    "moduleResolution": "node",
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "importHelpers": true,
    "target": "es2015",
    "typeRoots": [
      "node_modules/@types"
    ],
    "lib": [
      "es2018",
      "dom"
    ]
  }
}

[lppedd]

@alan-agius4 judging by your commit I suppose I could just add it to the tsconfig.json file, and it would be "equivalent". Am I right? How was it different in 7.* (I mean, here I was not targeting ES5)?
Btw, thanks for the quick response.

Edit: ok, I think I got it. It's because of differential loading.

[alan-agius4]

Yeah you are right 😊, thanks for brining this to our attention.

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