TypeScript Decorator - Log method calls

logdecorator.ts

function log(target, key, descriptor: PropertyDescriptor) {
	var originalMethod = descriptor.value;

    descriptor.value = function(...args: any[]) {
		let functionName = key;
		console.log(functionName + "(" + args.join(", ") + ")");
        let result = originalMethod.apply(this, args);
        console.log("=> " + result);
        return result;
    };

    return descriptor;
}

class Person {
	@log
	greet(name: string): string {
		return `hello ${name}`;
	}
}

new Person().greet("world");

result is

greet(world)
=> hello world