Deno 2.0 Decorators

[cfjello]

I have some older decorators with parameters that used to work in Deno/Typescript, here illustrated with a simple example:

function PluginDecorator(name: string) {
    return (_ctor: () => void) => {
        console.log("Plugin found: " + name);
    }
}

@PluginDecorator("My first Plugin")
class myFirstPlugin {
   
}

It now gives me an error:

Unable to resolve signature of class decorator when called as an expression.
  The runtime will invoke the decorator with 2 arguments, but the decorator expects 1.deno-ts(1238)

In Deno 2.0 the following options are depreciated:

{
    "compilerOptions": {
        "emitDecoratorMetadata": true,
        "experimentalDecorators": true 
    }
}

and now gives me Value is deprecated, and I have not been able to find a work around for this. Can somebody please advise, it would much appreciated, best of all if you could provide me with a small working example?

[bartlomieju]

With the Value is deprecated warning does the decorator work as expected?

[cfjello]

It does not work, unfortunately. I investigated a little bit further using Typescript tsc instead of Deno, with and without the flags, but it also errors, so it seems to be an issue originating in Typescript. I will opt for writing some mixin-functions instead.

[nathanwhit]

I don't fully understand why, or when this changed, but the issue is with the typing of the argument to your decorator. You have it typed as () => void, but typescript will be passing a class type to it. Instead you should type it as { new (): void } or new () => void.

So

function PluginDecorator(name: string) {
    return (_ctor: new () => void) => { // note the insertion of `new`
        console.log("Plugin found: " + name);
    }
}

@PluginDecorator("My first Plugin")
class myFirstPlugin {
   
}

This works, but as per the example in the typescript reference on class decorators (it's the example at the end of the Class Decorators section) I think the most correct typing would be more like

function PluginDecorator(name: string) {
    return <T extends { new (...args: any[]): {} }>(_ctor: T) => {
        console.log("Plugin found: " + name);
    }
}

[cfjello]

Great! They both work without any flags in my setup with the newest Deno v.2.0..5, even though the vscode Deno linter still complans: "Unable to resolve signature of class decorator ....". Thanks!