json - JavaScript Serialization and Methods

Question

I am new to "object-oriented" JavaScript. Currently, I have an object that I need to pass across pages. My object is defined as follows:

function MyObject() { this.init(); }
MyObject.prototype = {
    property1: "",
    property2: "",

    init: function () {
        this.property1 = "First";
        this.property2 = "Second";
    },

    test: function() {
      alert("Executing test!");
    }
}

On Page 1 of my application, I am creating an instance of MyObject. I am then serializing the object and storing it in local storage. I am doing this as shown here:

var mo = new MyObject();
mo.test();                                    // This works
window.localStorage.setItem("myObject", JSON.stringify(mo));

Now, on Page 2, I need get that object and work with it. To retrieve it, I am using the following:

var mo = window.localStorage.getItem("myObject");
mo = JSON.parse(mo);
alert(mo.property1);    // This shows "First" as expected.
mo.test();              // This does not work. In fact, I get a "TypeError"  that says "undefined method" in the consol window.

Based on the outputs, it looks like when I serialized the object, somehow the functions get dropped. I can still see the properties. But I can't interact with any of my functions. What am I doing wrong?

Answer 1

JSON doesn't serialize functions.

Take a look at the second paragraph here.

If you need to preserve such values, you can transform values as they are serialized, or prior to deserialization, to enable JSON to represent additional data types.

In other words, if you really want to JSONify the functions, you can convert them to strings before serializing:

mo.init = ''+mo.init;
mo.test = ''+mo.test;

And after deserializing, convert them back to functions.

mo.init = eval(mo.init);
mo.test = eval(mo.test);

However, there should be no reason to do that. Instead, you can have your MyObject constructor accept a simple object (as would result from parsing the JSON string) and copy the object's properties to itself.