proxy_monitor.ts

const consoleLogger = (...args: unknown[]) => {
  console.log(...args);
};

const consoleTracer = (...args: unknown[]) => {
  console.trace(...args);
};
type MonitorAction = "get" | "set";
type MonitorDesc<T> = [prop: keyof T, ...actions: MonitorAction[]];

const monitor = <T extends object>(
  logger: (...args: unknown[]) => void,
  ...descriptions: MonitorDesc<T>[]
): ProxyHandler<T> => {
  const shouldLog = (prop: PropertyKey, action: MonitorAction) => {
    return descriptions.some(
      ([dProp, ...actions]) => dProp === prop && actions.indexOf(action) > -1
    );
  };
  return {
    get: (target, prop: keyof T) => {
      if (shouldLog(prop, "get")) {
        logger("GET: " + String(prop), target[prop], target);
      }
      return target[prop];
    },
    set: (target, prop: keyof T, val) => {
      if (shouldLog(prop, "set")) {
        logger("SET: " + String(prop), val, target[prop], target);
      }
      target[prop] = val;
      return true;
    },
  };
};

const x = new Proxy(
  { id: 7, data: "foo" },
  monitor(consoleLogger, ["id", "get"], ["data", "set", "get"])
);

x.id; // GET: id 7 {id: 7, data: "foo"}
x.id = 10;
x.data; // GET: data foo {id: 10, data: "foo"}
x.data = "baz"; // SET: data baz foo {id: 10, data: "foo"}