How to restore original object/type from JSON?

Question

Its easy to load JSON into an object in javascript using eval or JSON.parse.

But if you have a proper \"class\" like function, how do you get the JSON data into it?<

Answer 1

A little late to the party, but this might help someone. This is how I've solved it, ES6 syntax:

class Page 
{
   constructor() {
      this.__className = "Page";
   }

   __initialize() {
       // Do whatever initialization you need here.
       // We'll use this as a makeshift constructor.
       // This method is NOT required, though
   }
}

class PageSection
{
   constructor() {
      this.__className = "PageSection";
   }
}

class ObjectRebuilder
{
    // We need this so we can instantiate objects from class name strings
    static classList() {
        return {
            Page: Page,
            PageSection: PageSection
        }
    }

    // Checks if passed variable is object.
    // Returns true for arrays as well, as intended
    static isObject(varOrObj) {
        return varOrObj !== null && typeof varOrObj === 'object';
    }

    static restoreObject(obj) {
        let newObj = obj;

        // At this point we have regular javascript object
        // which we got from JSON.parse. First, check if it
        // has "__className" property which we defined in the
        // constructor of each class
        if (obj.hasOwnProperty("__className")) {
            let list = ObjectRebuilder.classList();

            // Instantiate object of the correct class
            newObj = new (list[obj["__className"]]);

            // Copy all of current object's properties
            // to the newly instantiated object
            newObj = Object.assign(newObj, obj);

            // Run the makeshift constructor, if the
            // new object has one
            if (newObj.__initialize === 'function') {
                newObj.__initialize();
            }
        }

        // Iterate over all of the properties of the new
        // object, and if some of them are objects (or arrays!) 
        // constructed by JSON.parse, run them through ObjectRebuilder
        for (let prop of Object.keys(newObj)) {
            if (ObjectRebuilder.isObject(newObj[prop])) {
                newObj[prop] = ObjectRebuilder.restoreObject(newObj[prop]);
            }
        }

        return newObj;
    }
}

let page = new Page();
let section1 = new PageSection();
let section2 = new PageSection();

page.pageSections = [section1, section2];

let jsonString = JSON.stringify(page);
let restoredPageWithPageSections = ObjectRebuilder.restoreObject(JSON.parse(jsonString));

console.log(restoredPageWithPageSections);

Your page should be restored as an object of class Page, with array containing 2 objects of class PageSection. Recursion works all the way to the last object regardless of depth.

@Sean Kinsey's answer helped me get to my solution.