"Error in Visual Studio: Identical global identifier found in Typescript code

I'm in the process of setting up a visual studio solution using angular 2. Initially, I'm creating the basic program outlined in this tutorial: https://angular.io/docs/ts/latest/guide/setup.html

These are the three TS files that have been generated:

inventory.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule }      from '@angular/core';
import { InventoryComponent } from './inventory.component'

@NgModule({
  imports: [BrowserModule],
  declarations: [InventoryComponent],
  bootstrap: [InventoryComponent]
})

export class InventoryModule {
}

inventory.component.ts

import { Component } from '@angular/core';

@Component({
  selector: 'inventory',
  template: `<h1>Hello {{name}}</h1>`
})
export class InventoryComponent { name = 'Angular'; }

inventory.boot.ts

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';
import { InventoryModule }              from './inventory.module';

platformBrowserDynamic().bootstrapModule(InventoryModule);

When running the application in Chrome, I encounter the following error: inventory.module.js:12 Uncaught SyntaxError: Identifier 'core_1' has already been declared

This issue arises due to import statements in TypeScript all transposing to a line like this: const core_1 = require('@angular/core');

Consequently, multiple files contain these globally declared constants, each transposed with the name core_1.

Evidently, there might be a workaround for this problem, but my search efforts have been fruitless. Can anyone provide some advice? Thank you in advance!

EDIT Upon request, here is my TypeScript config: tsconfig.json

{
  "compilerOptions": {
    "module": "commonjs",
    "target": "es6",
    "noImplicitAny": true,
    "sourceMap": true,
    "experimentalDecorators": true
  }
}

Furthermore, certain properties in the .csproj file may apply:

<TypeScriptModuleKind>CommonJs</TypeScriptModuleKind>
<TypeScriptCompileOnSaveEnabled>True</TypeScriptCompileOnSaveEnabled>
<TypeScriptEmitDecoratorMetadata>True</TypeScriptEmitDecoratorMetadata>
<TypeScriptExperimentalDecorators>True</TypeScriptExperimentalDecorators>
<TypeScriptGeneratesDeclarations>False</TypeScriptGeneratesDeclarations>
<TypeScriptJSXEmit>None</TypeScriptJSXEmit>
<TypeScriptModuleResolution>Node</TypeScriptModuleResolution>
<TypeScriptNoEmitOnError>True</TypeScriptNoEmitOnError>
<TypeScriptNoImplicitAny>True</TypeScriptNoImplicitAny>
<TypeScriptRemoveComments>True</TypeScriptRemoveComments>
<TypeScriptSourceMap>True</TypeScriptSourceMap>
<TypeScriptTarget>ES6</TypeScriptTarget>

To clarify some of these choices

  • The target ES6 is chosen because I encountered compiler errors in Visual Studio when referencing angular2 (which depends on ES6 objects such as Promise).
  • Module Resolution is set to Node as I require tsc to navigate the node tree to access the references to angular 2.
  • The Module kind was initially AMD, but it had to be changed to CommonJs since I received the runtime error "define is not defined" in the browser.

Answer №1

If you're encountering duplicate identifier errors, it could be due to the fact that each of your CommonJS modules is perceived to have the same scope by the browser. In environments like Node.js, individual files are typically assumed to have their own scopes.

Additionally, the declarations emitted by TypeScript are usually in the form of const, which can lead to JavaScript throwing errors when it encounters multiple instances of let or const with the same name.

In my case, I initially set the Module kind to AMD, but had to switch it to CommonJS because I faced an error stating "define is not defined" during runtime in the browser.

This issue might arise if you haven't included and configured an AMD loader (e.g., Require.js) on your webpage.

To effectively utilize modules in the browser, consider employing a module loader or bundler such as System.js for SystemJS, Require.js for AMD, or Webpack/Browserify for CommonJS.

  1. If working with systemjs, opt for System.js.
  2. If targeting AMD, go for Require.js.
  3. If utilizing CommonJS, consider using Webpack or Browserify.

For System.js and AMD setups, ensure to include a <script> tag and configure it properly on your page.

I aimed for ES6 compatibility, as compiler errors emerged in Visual Studio while referencing Angular 2, which relies on ES6 features like Promise.

While opting for ES6 seems logical at first glance, keep in mind that older browsers may not support ES6 constructs. In such cases, targeting ES5 would be a more practical choice. However, should you choose to incorporate a Promise polyfill (e.g., core-js or es6-shim), adjust your lib setting or MSBuild <TypeScriptLib> to include:

dom,es2015,es5

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