In node.js, how to store objects (with methods) into file or db?

I want to store objects (with methods) in to file or DB. For example

var fs = require('fs');

function Worker(name, age){
    this.name = name;
    this.age = age;
}

Worker.prototype.work = function(){
    console.log("I am working...");
}

worker = new Worker("Alice", 20);
worker.work();

fs.writeFile(
   "worker.json",
    JSON.stringify(worker),
    function(){}
);

When I read the JSON file I can load the "work()" method:

fs.readFile("worker.json", function(err, data) {
    worker = JSON.parse(data);
    worker.work(); // I am working...
}

How can I achieve this?