Typescript method is return undefined with method decorator

I apologize if it is a silly question. I am new with typescript and learning typescript decorators. I found a code: MethodDecorator to log the arguments and the result.

log decorator

function log (target: Object, key: string, descriptor: TypedPropertyDescriptor<any>) {    let originalMethod = descriptor.value;    descriptor.value = function (...args:any[]) {        //before        console.log(`${key} method called with args: ${JSON.stringify(args)}`);        let result = originalMethod.apply(this, args);        //after        console.log(`${key} method return value: ${JSON.stringify(result)}`);    }    return descriptor;}

I am using @log with setId and getId methods in Book class

book.ts

class Book{    constructor(public id: number, public title: string, public publisher: string){}    @log    setId(id: number){        this.id = id;    }    @log    getId(): number{        return this.id;    }}

All code works fine but getId returns undefined when i run this code.

let book = new Book(1, "Learn TypeScript", "O\'Reilly Media");let favBookId = book.getId();console.log("Book before setId: ");console.log(book);console.log("Favourite book id: "+favBookId);book.setId(5);console.log("Book after setId: ");console.log(book);console.log("Favourite book id: "+favBookId);

my tsconfig.json

{"compilerOptions": {"target": "es5","module": "commonjs","removeComments": false,"experimentalDecorators": true    }}

To compile and run:

tsc -p ./node book.js

Output:

getId method called with args: []getId method return value: 1Book before setId:Book {id: 1, title: 'Learn TypeScript', publisher: 'O\'Reilly Media' }Favourite book id: undefinedsetId method called with args: [5]setId method return value: undefinedBook after setId:Book {id: 5, title: 'Learn TypeScript', publisher: 'O\'Reilly Media' }Favourite book id: undefined

I am not able to understand why setId is working as I want and getId is not??

tsc -v: Version 1.8.10