Typescript error :TS2304 cannot find name

Question

Burning through a typescript course I came across these code pieces that fail to compile and give error TS2304. Any help is appreciated.

file ZooAnimals.ts:

namespace Zoo {
    interface Animal {
        skinType: string;
        isMammal(): boolean;
    }
}

File ZooBirds.ts:

/// <reference path="ZooAnimals.ts" />
namespace Zoo {
    export class Bird implements Animal {
        skinType = "feather";
        isMammal() {
            return false;
        }
    }
}

The command to compile the files:

tsc --outFile Zoo.js ZooAnimals.ts ZooBirds.ts

Throws error:

ZooBirds.ts:3:34 - error TS2304: Cannot find name 'Animal'.

3     export class Bird implements Animal {

Titian Cernicova-Dragomir · Accepted Answer · 2019-03-02 18:15:49Z

2

To use the interface across files (or more precisely across multiple namespace declarations) it must be exported (even if it is part of the same namespace). This will work:

namespace Zoo {
    export interface Animal {
        skinType: string;
        isMammal(): boolean;
    }
}
namespace Zoo {
    export class Bird implements Animal {
        skinType = "feather";
        isMammal() {
            return false;
        }
    }
}

answered Mar 2, 2019 at 18:15

Titian Cernicova-Dragomir

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4 Comments

rks Over a year ago

That certainly works - thanks. The edX course (from Microsoft) suggests to use '/// <reference path='...' /> ' tag to resolve the inclusion of the Animal definition and not export the interface. But somehow the reference path does not seem to be working. Wondering if I am doing something wrong or the version of typescript that can only work as suggested by you.

Titian Cernicova-Dragomir Over a year ago

@rks The <reference...> might still be needed for the definitions to be discovered. But the export is most definitely required..

rks Over a year ago

Actually it works without needing the <reference .../> tag if the interface is exported. Here is the code from the course: ZooAnimals.ts

namespace Zoo {	     interface Animal { //note that we do not need the *export* here since this interface will only be accessible only by entities from within the Zoo namespace 		 skinType: string;         isMammal(): boolean;     } }

Titian Cernicova-Dragomir Over a year ago

@rks it should work without the ///<ref as well if all the files are included in the compilation .. it was probably an oversight in the course..

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