I'm experiencing issues with duplicated Typescript type declarations in the following case:

I've got the following dependency tree for my application A:

A->@angular/http:2.3.1
A->B->@angular/http:2.3.1

Both A and B are managed by npm. After running

npm install

the filesystem looks like this:

A/node_modules/
  @angular/http
  ...
  B/node_modules
     @angular/http

The problem seems to be that now there are two type declarations of @angular/http types like Response, or Headers. And somehow the Typescript transpiler seems unable to handle that - resulting in the following error message:

TS2453:The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly. Type argument candidate 'Response' is not a valid type argument because it is not a supertype of candidate 'Response'. Types of property 'headers' are inpatible. Type 'Headers' is not assignable to type 'Headers'. Types have separate declarations of a private property 'mayBeSetNormalizedName'.

Reading the message, I guess this is a hickup of Typescript not being able to match the duplicated type declarations.

Anybody experienced the same issue? How to handle that problem? How to handle such name collisions?

I'm experiencing issues with duplicated Typescript type declarations in the following case:

I've got the following dependency tree for my application A:

A->@angular/http:2.3.1
A->B->@angular/http:2.3.1

Both A and B are managed by npm. After running

npm install

the filesystem looks like this:

A/node_modules/
  @angular/http
  ...
  B/node_modules
     @angular/http

The problem seems to be that now there are two type declarations of @angular/http types like Response, or Headers. And somehow the Typescript transpiler seems unable to handle that - resulting in the following error message:

TS2453:The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly. Type argument candidate 'Response' is not a valid type argument because it is not a supertype of candidate 'Response'. Types of property 'headers' are inpatible. Type 'Headers' is not assignable to type 'Headers'. Types have separate declarations of a private property 'mayBeSetNormalizedName'.

Reading the message, I guess this is a hickup of Typescript not being able to match the duplicated type declarations.

Anybody experienced the same issue? How to handle that problem? How to handle such name collisions?

• javascript
• angular
• typescript
• npm

• I know there is this related question: stackoverflow./questions/42412938/…. The answer's not really satisfactory, because in my case I cannot (do not want to) simply move the sources from B into A. There must be another way. – Robert Commented Mar 20, 2017 at 17:13

2 Answers 2

Meanwhile I found out that you can fix this error by explicitly importing the according types inside the using class of A. In my case (cp. error message above), I needed to:

import {Response, Headers} from '@angular/http';

I had the same problem. There are basically two ways to solve this.

1. Make a UMD module of project B. This might take a lot of time
2. use as any as TheRequiredObject see below.

Let assume you got this class in project b:

export class B{
    getSome(): Observable {
        return this.http.get('some_url');
    }
}

and this is what you want in project a:

export class A{
    getSomeFromB: Observable{
        return B.getSome() as any as Observable;
    }
}