Angular: 7.2.1 ES6 class ReferenceError : Cannot access 'X' before initialization

问题

I'm having the following TypeScript class

export class Vehicule extends TrackableEntity {
  vehiculeId: number;
  constructor() {
    super();
    return super.proxify(this);
  }
}

my typescript target in tsconfig.json is configured as es6:

"compilerOptions": {
    "module": "es2015",
    "moduleResolution": "node",
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "target": "es6",
}

At runtime, here in Chrome, the code is failing with:

ReferenceError: Cannot access 'Vehicule' before initialization
    at Module.Vehicule (https://localhost:44338/src-app-components-dispositifsDATI-dispositifsDATI-module.js:10559:100)
    at Module../src/app/domain/models/VehiculeGpsBoxInfo.ts (https://localhost:44338/src-app-components-dispositifsDATI-dispositifsDATI-module.js:11156:69)
    at __webpack_require__ (https://localhost:44338/runtime.js:84:30)
    at Module../src/app/domain/models/Vehicule.ts (https://localhost:44338/src-app-components-dispositifsDATI-dispositifsDATI-module.js:10571:78)
    at __webpack_require__ (https://localhost:44338/runtime.js:84:30)
    at Module../src/app/components/dispositifsDATI/mainDATI/listDATI/listDATI.component.ts (https://localhost:44338/src-app-components-dispositifsDATI-dispositifsDATI-module.js:6447:82)
    at __webpack_require__ (https://localhost:44338/runtime.js:84:30)
    at Module../src/app/components/dispositifsDATI/index.ts (https://localhost:44338/src-app-components-dispositifsDATI-dispositifsDATI-module.js:3053:95)
    at __webpack_require__ (https://localhost:44338/runtime.js:84:30)
    at Module../src/app/components/dispositifsDATI/dispositifsDATI.routes.ts (https://localhost:44338/src-app-components-dispositifsDATI-dispositifsDATI-module.js:2982:64)

I needed to change es5 to es6 to solve this other problem.

EDIT: The VehiculeGpsBoxInfo.ts file is importing Vehicule like this:

import { Vehicule } from "./Vehicule";

EDIT 2: I vould say that this may be webpack related, the way that modules are exported/imported in the genrated modules.

EDIT 3: After further research, this seems to have nothing to do with the code shown above. Started a new question about webpack and ES6.

回答1:

You're probably running into this Angular issue: https://github.com/angular/angular-cli/issues/15077.

From that issue:

Hi, is there a reason why you need emitDecoratorMetadata to be true?

This TypeScript option has a fundamental design limitation with ES2015+ code and is best avoided when targeting such output. As such this is an issue with TypeScript itself and not Angular.

Angular 8+ no longer requires the option. It was also previously only required for JIT mode which is typically only used in development.

The solution is to set "emitDecoratorMetadata": false in your tsconfig.json file.

Side note: I must say, given that previous versions of the Angular CLI automatically added emitDecoratorMetadata: true, and there's no reason I can see why a dev should know that emitDecoratorMetadata should now be false, it's pretty horrible that the Angular team basically said "this isn't our problem" and closed the issue without action. This could have been easily "fixed" by adding some better documentation (as pointed out by someone in the linked issue).

回答2:

that make sense, you are passing the local object (Vehicle) to the parent class within constructor return super.proxify(this);.

Keep in mind the local Vehicle instance has not been instantiated yet (constructor block is not finished yet), so you cannot use this object in the mean time, you need to wait the constructor to done it's job.

来源：https://stackoverflow.com/questions/56870661/angular-7-2-1-es6-class-referenceerror-cannot-access-x-before-initializatio

标签

javascript

angular

typescript

Webpack

es6-class