Error occurs when trying to merge and export namespaces in TypeScript

I'm currently developing an app that utilizes TS and OpenLayers. In order to create a dependency tree, I have included import and export statements in my *.ts files.

One of the files is 'openlayers.ts', which extends the base OpenLayers library by adding functionalities to the openlayers interaction namespace.

Here is how my openlayers.ts file looks:

declare namespace ol {

    namespace interaction {
        interface someEvent {
            ...
        }

        class myExtendedClass extends ol.interaction.Pointer {
            ...
        }
    }
}

According to TypeScript documentation, the 'ol' namespace from the base OpenLayers library will merge with my extended 'ol' namespace. However, I encountered an issue when trying to export my extended namespace as it was not being recognized by the app without the export statement.

So, I modified my openlayers.ts file to look like this:

export declare namespace ol {

    ...
}

Within my 'ol' namespace, there is the 'myExtendedClass' which requires extension of 'ol.iteraction.Pointer' from the base OpenLayers.

After exporting the namespace, the app no longer recognizes 'ol.interaction.Pointer'. To resolve this, I concluded that I needed to import the base OpenLayers library into my file.

Therefore, my openlayers.ts now includes an import statement:

import ol = require('openlayers');

export declare namespace ol {

    ...
}

However, this resulted in errors:

  1. (TS) individual declarations in merged declaration 'ol' must be all exported or all local.
  2. At the 'ol.interaction.Pointer' - (TS) Property 'Pointer' does not exist on type 'typeof interaction'.
  3. (TS) Import declaration conflicts with local declaration of 'ol'

As a beginner in TypeScript, I am unsure of what steps I need to take next. The errors are quite confusing to me. Any suggestions?

Answer №1

After some diligent research and troubleshooting, I have successfully discovered the solution.

Throughout my journey, I encountered a few obstacles.

  1. One issue that arose was my confusion surrounding how my namespace extensions would function. Initially unsure whether to exclude these extensions from my openlayers.ts file or from the global OpenLayers reference, I delved deeper into TypeScript documentation and scoured the internet for possible resolutions. Eventually, it became clear that to extend a namespace, I must handle these extensions in a manner consistent with the original library structure. Much like extending strings or collections in C#, I had to avoid using MyStringExtenstion.SomeMethod(myString) and instead utilize myString.SomeMethod();
  2. I realized that there was no need to import OpenLayers into my openlayers.ts file due to the magic of namespace merging - when namespaces share identical names, they automatically merge. Consequently, I removed the line
    import ol = require('openlayers');
  3. The final challenge I faced involved exporting my extended namespace. Reflecting on this quandary, I came to the realization that since my namespaces seamlessly merged with the global OpenLayers namespaces, there was no requirement to export them again. As such, I modified export declare namespace ol to simply declare namespace ol.

In an effort to assist others who may encounter a similar dilemma, I will leave my question and answer intact so that those seeking a solution can do so more swiftly than I did.

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