How to read properties in typescript after using Object.defineProperty?

Question

I have the following code on typescript playground and a few questions come up that I am not sure how to get working

class PathInfo {
    functionName: string;
    httpPath: string;
    httpMethod: string;

    constructor(functionName: string, httpPath: string, httpMethod: string) {
        this.functionName = functionName;
        this.httpPath = httpPath;
        this.httpMethod = httpMethod;
    }

    toString(): string {
        return "PathInfo["+this.functionName+","+this.httpPath+","+this.httpMethod+"]";
    }
}

class AuthRequest {}
class AuthResponse {}
class LoginRequest {}
class LoginResponse {}

const path: any = (thePath: string, type: any) => {
    return (target: Function, memberName: string, propertyDescriptor: PropertyDescriptor) => {
        const pathMeta = new PathInfo(memberName, path, type);

        Object.defineProperty(target, memberName+'pathInfo', {
            value: pathMeta,
            writable: false
        });

        //How do I access the stored pathMeta
        //console.log("target="+target.pathInfo);
        console.log("member="+memberName);
        console.log("props="+propertyDescriptor);
    }
}

class AuthApiImpl {
    @path("/authenticate", AuthResponse)
    authenticate(request: AuthRequest): Promise<AuthResponse> {
        throw new Error("all this is generated by factory.createApiImpl");
    }
    @path("/login", LoginResponse)
    login(request: LoginRequest): Promise<LoginResponse> {
        throw new Error("all this is generated by factory.createApiImpl");
    }
};

function printMethods(obj: any) {
    console.log("starting to print methods");

  for (var id in obj) {
      console.log("id="+id);
    try {
      //How do I access the stored pathMeta here FOR EACH METHOD ->
      //console.log("target="+target.pathInfo);
      if (typeof(obj[id]) == "function") {
          console.log(id+":"+obj[id].toString());
      }
    } catch (err) {
      console.log(id + ": inaccessible"+err);
    }
  }

}

console.log("starting to run")

const temp = new AuthApiImpl();
printMethods(temp);

console.log("done")

• line 64-65, how to read the property that I set
• line 40-41, how to read the property that I set
• line 58-74, why is this not printing any functions? I want to print all functions and I do NOT want to print properties (just functions)
• line 33, Can I access the class name at this point?
• line 35, I thought target was a function and would be authorize, then login, BUT if I define the property as JUST 'pathInfo', I get an error that the property is already defined on the target(This implies the target is the class not the function?). I am so confused.

Terribly sorry as I try to focus on a single question, but this one test of writing decorators has given me more questions than answers as I delve into the typescript world.

How can I tweak the code to play more here?

A goal here is as developers define the APIs of other microservices, I can capture a bunch of meta information and store it SOMEWHERE I can use later in startup code. I do not care where I store that really, but just need a clean way of knowing the class I want to extend, the methods, the return types, the http path, etc.

Answer 1

How to get methods of a class

You still can't grab the method names even if you remove the decorator. This isn't a TypeScript specific question.

You need to get the properties of the prototype, not just the object itself.

function printMethods(obj: any) {
    console.log("starting to print methods");

    const objProto = Object.getPrototypeOf(obj);
    console.log(Object.getOwnPropertyNames(objProto));
}

How to access class names

Don't think this is possible with decorators at the moment, but it should be straightforward to just pass in your class name as a string.

Similar issue: TypeScript class decorator get class name

Open issue on GitHub: https://github.com/microsoft/TypeScript/issues/1579

"property is already defined on the target"

Notice if you run the code above you get the following in console.log:

["constructor", "authenticate", "login", "authenticatepathInfo", "loginpathInfo"]

I also want to point out that if you don't even initialize an instance of the class, you'll still get the same error.