JSDoc: unable to define an optional method on base class

[zombie]

TypeScript Version: 2.8.3

We have a base "abstract" (this is plain JS) class that defines an ExtensionAPI which extensions need to extend to provide the implementation. Some of the methods (like startup) are optional, and if not present, we can delay initializing the extensions on startup.

Typescript check complains that the base class doesn't have such methods, and the best solution I could figure out is to add a property to the ExtensionAPI.prototype and properly @type it, but that throws with error TS2425.

Code

class ExtensionAPI {
  run(file) {
    //
  }
}

/** @type {function(string): void} */
ExtensionAPI.prototype.startup = null;

///

class Linter extends ExtensionAPI {
  startup(file) {
    //
  }
  run(file) {
    //
  }
}

///

/** 
 * @param {ExtensionAPI[]} extensions
 */
function init(extensions, file) {
  for (let ext of extensions) {
    if (ext.startup) {
      ext.startup(file);
    }
  }  
}

init([new Linter()], "Utitled1");

Typecheck using:

tsc --allowjs --checkjs --noemit extensions.js

Actual behavior:

error TS2425: Class 'ExtensionAPI' defines instance member property 'startup', but extended class 'Linter' defines it as instance member function.

[mhegazy]

I think this is related to #22896, and #24467. I would say my proposal in #22896 (comment) should address the underlying use case.

[zombie]

Yes, that indeed sounds like a better solution, as long as it covers the above use case and doesn't throw "Class 'ExtensionAPI' defines instance member property 'startup', but extended class 'Linter' defines it as instance member function." (I'm not even sure when that error would be useful).

Hopefully that issue gets a milestone soon.

[sandersn]

@zombie Can you try this on 3.0 or newer? I don't get the error there.

[zombie]

Doesn't error anymore, thanks (and still looking forward to @property).