Node-ipc in Typescript class

Question

I am trying to use node-ipc in my TypeScript project and stuck on getting correct type for class member:

import { IPC } from 'node-ipc';

class IpcImpl extends IIpc {
    ipcSocketPath?: string;
    ipc?: any;  // What the type should be here?


    setupIpc(ipcSocketPath: string) {
        this.ipcSocketPath = ipcSocketPath;
        this.ipc = new IPC();  // Here instantiated ok, but type mismatch ed

    }

I of course installed @types/node-ipc but it doesn't helped me. I tried to specify following (everything incorrect):

• ipc?: IPC
• ipc?: typeof IPC

How to specify type of my ipc class member right?

Answer 1

From the node-ipc's index.d.ts content, you can not use the NodeIPC namespace or NodeIPC.IPC class directly as they are not exported:

declare namespace NodeIPC {
    class IPC {
        // Some methods
    }
    // Some other classes
}

declare const RootIPC: NodeIPC.IPC & { IPC: new () => NodeIPC.IPC };

export = RootIPC;

But, if you are using TypeScript 2.8+, you should be able to infer the type thanks to the conditional types and the type inference using in your case:

type InferType<T> = T extends new () => infer U ? U : undefined;

And so you can get the NodeIPC.IPC type:

import { IPC } from 'node-ipc';

type InferType<T> = T extends new () => infer U ? U : undefined;

class IpcImpl {

    ipcSocketPath?: string;
    ipc?: InferType<typeof IPC>;

    setupIpc(ipcSocketPath: string) {
        this.ipcSocketPath = ipcSocketPath;
        this.ipc = new IPC();
    }

}

You can find some interresting information about the conditional types and type inference in the TypeScript 2.8 release notes: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-8.html

Update:

I just found out that TypeScripts's 2.8+ includes the InstanceType<T> predefined conditional type which does exactly the same thing than the InferType<T> from my code above. So in fact, use it directly and we have an even shorter solution:

class IpcImpl {

    ipcSocketPath?: string;
    ipc?: InstanceType<typeof IPC>;

    setupIpc(ipcSocketPath: string) {
        this.ipcSocketPath = ipcSocketPath;
        this.ipc = new IPC();
    }

}