javascript : save function to object

Question

I saved a function in an Object.

var obj = {
  name: 'bob',
  getName: function() {
    return this.name;
  }
};
console.log(obj.getName());

It shows 'bob'. But when I saved this obj to Session or MongoDB, the function was disappeared.

Session.set('tmp', obj);
var tmpObj = Session.get('tmp');
console.log(tmpObj.getName());

This shows undefined.

I've tested JSON.stringify / parse also, it doesn't work.

How can I keep the function in the object?

Answer 1

In most contexts you cannot save functions. Try putting all variables into primitive properties instead, and after reloading the "dumb" object, reinitialize with methods like this:

var ObjMaker = function(attrs){
  this.name = attrs.name;
}

ObjMaker.greet = function(){
  return 'Hello ' + this.name;
}

var reloadedObj = { name: 'bob' };

var obj = new Obj(reloadedObj);

console.log(obj.greet());

Answer 2

In most cases it is not possible. Technically you can serialize a function using obj.getName.toString() , which should return

function() {
    return this.name;
}

You could then run it with something like eval("(" + functionString + ")()") . But this pretty much always a bad idea.

If you want to store it into MongoDB, you probably want to use Mongoose ODM , and custom setter . This allows you to define a function on a Schema that describes objects stored in MongoDB, which should fulfill your needs.

var objSchema = new Schema({
  name: {
    type: String,
    get: function(name) {
      return name; //Of course, you could manipulate this more if you want.
    }
  }
});