Typescript namespace undefined when referenced in a file

Question

declare namespace Space.NewSpace {
    enum TestEnum {
        Foo,
        Bar
    }
}

in my .tsx file I'm trying to use the enum as follows:

Space.NewSpace.TestEnum.Foo

But it's throwing this error: Uncaught TypeError: Cannot read property 'Space' of undefined

Try getting rid of declare? Unless you're importing the namespace from somewhere else? — Erty Seidohl
– Erty Seidohl, Commented Sep 6, 2019 at 3:54
If I remove it, it says Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier. — blankface
– blankface, Commented Sep 6, 2019 at 5:50

ford04 · Accepted Answer · 2019-09-07 07:26:58Z

3

Your TypeError is a JavaScript runtime error and not (directly) related to TS type system.

When you use declare namespace, you expect a third party library script to provide the namespace/property on the global namespace for you at runtime. declare xxx keyword is only relevant for compile type, e.g. to make global variables known for TS compiler. If there is no global property provided later on, you get above error.

So, if you have a third party namespace you depend on, you'll want to write:

declare namespace Space.NewSpace {
  enum TestEnum {
    Foo,
    Bar
  }
}

... and the library would provide the namespace similar to this:

var Space = {
  NewSpace: {
    // enum simplified here
    TestEnum: {"0": "Foo", "1": "Bar", Foo: 0, Bar: 1}
  }
};

If you write a namespace for your own code, leave out the declare keyword and export the members.

namespace Space.NewSpace {
  export enum TestEnum {
    Foo,
    Bar
  }
}

console.log(Space.NewSpace.TestEnum[0]); // Foo

edited Sep 7, 2019 at 7:26

answered Sep 6, 2019 at 6:59

ford04

75.8k26 gold badges219 silver badges176 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

blankface Over a year ago

removing declare throws this error: Top-level declarations in .d.ts files must start with either a 'declare' or 'export' modifier.

ford04 Over a year ago

@ZeroDarkThirty ...because you have to use declare, when you want to define an ambient (without implementation) namespace in a .d.ts file. Does this sample repo help?

blankface Over a year ago

ah so you're saying if i have a namespace with implementation (like my original post), it can't have the declare keyword? in that case do i need the actual implementation in another namespace (minus declare keyword)?

ford04 Over a year ago

yes. and in this case, just write the implementation (namespace xxx) and drop the declaration (declare namespace xxx) entirely.

Collectives™ on Stack Overflow

Typescript namespace undefined when referenced in a file

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related