VS2019 error TS2300: Duplicate identifier IteratorResult

user_776539 0
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I have an ASP.NET Core Project with Angular App inside it. After updating the project to .NET Core 3.0 release, I've got a problem. During ASP.NET Core Project build, I see 2 errors in the output:

1>------ Build started: Project: Portal, Configuration: Debug Any CPU ------
1>C:\Program Files (x86)\Microsoft SDKs\TypeScript\3.6\lib.es2015.iterable.d.ts(41,6): error TS2300: Build:Duplicate identifier 'IteratorResult'.
1>D:\Solution\MyProject\ClientApp\node_modules\@types\node\index.d.ts(73,11): error TS2300: Build:Duplicate identifier 'IteratorResult'.
1>MyProject -> D:\Solution\MyProject\bin\Debug\netcoreapp3.0\Portal.dll
1>Done building project "Portal.csproj".
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

package.json:

{
  "name": "client-app",
  "version": "0.0.0",
  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e",
    "build-dev": "ng build --configuration=development"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "^8.2.2",
    "@angular/cdk": "~8.1.3",
    "@angular/common": "~8.2.0-next.1",
    "@angular/compiler": "~8.2.0-next.1",
    "@angular/core": "~8.2.0-next.1",
    "@angular/forms": "~8.2.0-next.1",
    "@angular/platform-browser": "~8.2.0-next.1",
    "@angular/platform-browser-dynamic": "~8.2.0-next.1",
    "@angular/router": "~8.2.0-next.1",
    "core-js": "^2.5.4",
    "primeflex": "^1.0.0-rc.1",
    "primeicons": "^1.0.0",
    "primeng": "^8.0.1",
    "rxjs": "~6.5.2",
    "tslib": "^1.9.0",
    "zone.js": "~0.9.1"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "~0.801.1",
    "@angular/cli": "~8.1.1",
    "@angular/compiler-cli": "~8.2.0-next.1",
    "@angular/language-service": "~8.2.0-next.1",
    "@types/node": "~8.9.4",
    "@types/jasmine": "~2.8.8",
    "@types/jasminewd2": "~2.0.3",
    "codelyzer": "^5.0.1",
    "jasmine-core": "~2.99.1",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~4.0.0",
    "karma-chrome-launcher": "~2.2.0",
    "karma-coverage-istanbul-reporter": "~2.0.1",
    "karma-jasmine": "~1.1.2",
    "karma-jasmine-html-reporter": "^0.2.2",
    "protractor": "~5.4.0",
    "ts-node": "~7.0.0",
    "tslint": "~5.11.0",
    "typescript": "3.4.5"
  }
}

tsconfig.json:

{
  "compileOnSave": false,
  "compilerOptions": {
    "baseUrl": "./",
    "downlevelIteration": true,
    "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"
    ]
  }
}

What I tried:

  • update @type/node through npm;
  • delete @type/node from package.json;
  • change typescript (bottom of package.json) version to 3.6.4.
visual-studio-2019 angular asp.net-core build
5 Answers

I also had exactly the same problem with Vs2019 and angular version 8. I have tried as suggested above downloading and installing TypesScript compiler version 3.7 for VS2019. But the problem persisted.

The only way I solved the above problem as per J King's recommendation of upgrading node types higher than or equal to version 8.10.52. In then tsconfig.json file I have set the compiler target version to ES6. Then issued the following commands:

npm install @types/node@8.10.52

then do:

ng build

Make sure it builds cleanly. The do a clean build in Vs2019.

This seems to solve the problem.

user_122005470

Angular 8 wants Typescript >= 3.4.0 and < 3.6.0, but Visual Studio 2019 builds using 3.7.

I was able to fix these issues by installing 3.5.3 in both NPM and Visual Studio.

npm install --save typescript@3.5

Install-Package Microsoft.TypeScript.MsBuild -Version 3.5.3

After that the Typescript version dropdown in project properties (TypeScript Build tab) is grayed out, but reads the correct value of 3.5 (NuGet). Saved, rebuilt and all was good.

Hope that helps someone. I spent 4 hours trying to fix this.

Aaron

user_8864320

I also got similar issue, but after installing Typescript on local machine from below link, http://www.typescriptlang.org/#download-links

I rebuild solution, it worked.

Note : Choose your appropriate VisualStudio version or any IDE you are using from download link!

user_57902750

I faced this issue a couple of times. Once I was able to solve it using the way recommended by @wkkhondkar, the other time I realized the issue was because of the fact that I executed the command ng run serve for the SPA and forgot to stop the server.

user_25087840

I guess it is showing the error because somewhere you try to reinitialize the same property twice or more times.

For Example:

let name = "John";
let person = {
    name,
    name: "Jane"
}

As in the above code,

  • we first assigned the person's property(name) to John.
  • but then we reassigned the person's property(name) to Jane.

This will make the first initialization redundant.

Result : person = {name: "Jane"}

user_101206490
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