Symbol.metadata is undefined

[sant123]

Version: Deno 1.40.1

Thanks.

[crowlKats]

What are you expecting this would do? No browser, nor node, implement a Symbol.metadata.

[sant123]

Consider this example:

function bind(_: unknown, ctx: ClassMethodDecoratorContext<any>) {
  ctx.addInitializer(function () {
    this[ctx.name] = this[ctx.name].bind(this);
  });
}

class Person {
  constructor(private firstName: string, private lastName: string) {}

  @bind
  greet() {
    console.log(`Hellou ${this.firstName} ${this.lastName}`);
  }

  @bind
  static start() {
    console.log("Hello World!", this);
  }
}

Person.start();

It prints:

Perhaps it should print the empty object shown in the console meanwhile?

[bartlomieju]

I also don't understand what's the problem here. Where is the Symbol(Symbol.metadata) coming from in your example?

[sant123]

It comes directly from the runtime, so the metadata exists but is not exposed? I got curious about that data in the console.

[Jamesernator]

I also don't understand what's the problem here. Where is the Symbol(Symbol.metadata) coming from in your example?

Symbol.metadata is part of decorator metadata, the use of any decorators on a class add the metadata object to the class.

What are you expecting this would do? No browser, nor node, implement a Symbol.metadata.

Given Deno supports decorators in TypeScript it should expose the symbol, Deno already supports Symbol.dispose/Symbol.asyncDispose which are from another proposal not implemented in browsers either.

[lucacasonato]

Yeah, I checked and SWC does transpile decorator metadata. We should polyfill Symbol.metadata like we do for Symbol.dispose