TypeScript: Duplicate identifier 'IteratorResult'

Question

I\'m trying to compile via tsc--which I\'ve installed globally--and I\'m getting an error:

~/AppData/R         


        

Answer 1

For me it turned out I had a node_modules folder in a parent directory project, something similar to this:

node_modules
my-project
- node_modules

Since the node_modules had an older version of @types/node installed, the problem happened. In my case the solution however wasn't to update @types/node but instead to remove those node_modules since I wasn't using them in the first place.

If you actually need to have a node_modules in a parent directory with different types and this is how you want it to be, then you can specify the typeRoots specifically:

{
  "compilerOptions": {
    "module": "esnext",
    "target": "es6",
    "declaration": true,
    "outDir": "./dist",
    "typeRoots": ["./node_modules/@types/"]
  },
  "include": [
    "src/**/*"
  ]
}

That way, the parent node_modules aren't scanned for types. Otherwise they are, read here: https://www.typescriptlang.org/docs/handbook/tsconfig-json.html#types-typeroots-and-types

By default all visible “@types” packages are included in your compilation. Packages in node_modules/@types of any enclosing folder are considered visible; specifically, that means packages within ./node_modules/@types/, ../node_modules/@types/, ../../node_modules/@types/, and so on.

Answer 2

I found this thread after googling the error. My problem was that somehow I had an unneeded import which caused this:

import { error } from 'protractor';

Answer 3

I resolved this issue manually by commenting one of the interface "IteratorResult" declaration in node_modules/@types/node/index.d.ts file. Hope this will help.

Answer 4

I suspect it is because your include section:

"include": [
    "app/**/*.ts",
    "app/**/*.tsx",
    "test/**/*.ts",
    "test/**/*.tsx",
    "node_modules/@types/**/*.d.ts",
    "./types/**/*.d.ts"
  ]

You usually don't need to explicitly include *.d.ts files. And probably never declaration files from other libraries (or node types).

tsconfig's "exclude" section excludes everything under "node_modules" by default (among other things). When you add "node_modules/@types/**/*.d.ts" you override that exclude and tsc tries to include them, but those types are already declared.

Check Typescript docs on tsconfig.json, it explains the "typeRoots", "files" and "include"/"exclude" config options in detail.

Answer 5

This is how I solved it:

npm uninstall --save-dev webpack

npm install --save-dev @angular-devkit/build-angular@latest

Answer 6

Add "skipLibCheck": true in compilerOptions in tsconfig.json.

This solved the issue. Check here