How to use javascript proxy for nested objects

Question

I have this code in js bin:

var validator = {
  set (target, key, value) {
    console.log(target);
    console.log(key);
    console.log(value);
    if(isO         


        

Answer 1

I have also created a library type function for observing updates on deeply nested proxy objects (I created it for use as a one-way bound data model). Compared to Elliot's library it's slightly easier to understand at < 100 lines. Moreover, I think Elliot's worry about new Proxy objects being made is a premature optimisation, so I kept that feature to make it simpler to reason about the function of the code.

observable-model.js

let ObservableModel = (function () {
    /*
    * observableValidation: This is a validation handler for the observable model construct.
    * It allows objects to be created with deeply nested object hierarchies, each of which
    * is a proxy implementing the observable validator. It uses markers to track the path an update to the object takes
    *    is an array of values representing the breadcrumb trail of object properties up until the final get/set action
    *    the earliest property in this  which contained an observers array    *
    */
    let observableValidation = {
        get(target, prop) {
            this.updateMarkers(target, prop);
            if (target[prop] && typeof target[prop] === 'object') {
                target[prop] = new Proxy(target[prop], observableValidation);
                return new Proxy(target[prop], observableValidation);
            } else {
                return target[prop];
            }
        },
        set(target, prop, value) {
            this.updateMarkers(target, prop);
            // user is attempting to update an entire observable field
            // so maintain the observers array
            target[prop] = this.path.length === 1 && prop !== 'length'
                ? Object.assign(value, { observers: target[prop].observers })
                : value;
            // don't send events on observer changes / magic length changes
            if(!this.path.includes('observers') && prop !== 'length') {
                this.rootTarget.observers.forEach(o => o.onEvent(this.path, value));
            }
            // reset the markers
            this.rootTarget = undefined;
            this.path.length = 0;
            return true;
        },
        updateMarkers(target, prop) {
            this.path.push(prop);
            this.rootTarget = this.path.length === 1 && prop !== 'length'
                ? target[prop]
                : target;
        },
        path: [],
        set rootTarget(target) {
            if(typeof target === 'undefined') {
                this._rootTarget = undefined;
            }
            else if(!this._rootTarget && target.hasOwnProperty('observers')) {
                this._rootTarget = Object.assign({}, target);
            }
        },
        get rootTarget() {
            return this._rootTarget;
        }
    };

    /*
    * create: Creates an object with keys governed by the fields array
    * The value at each key is an object with an observers array
    */
    function create(fields) {
        let observableModel = {};
        fields.forEach(f => observableModel[f] = { observers: [] });
        return new Proxy(observableModel, observableValidation);
    }

    return {create: create};
})();

It's then trivial to create an observable model and register observers:

app.js

// give the create function a list of fields to convert into observables
let model = ObservableModel.create([
    'profile',
    'availableGames'
]);

// define the observer handler. it must have an onEvent function
// to handle events sent by the model
let profileObserver = {
    onEvent(field, newValue) {
        console.log(
            'handling profile event: \n\tfield: %s\n\tnewValue: %s',
            JSON.stringify(field),
            JSON.stringify(newValue));
    }
};

// register the observer on the profile field of the model
model.profile.observers.push(profileObserver);

// make a change to profile - the observer prints:
// handling profile event:
//        field: ["profile"]
//        newValue: {"name":{"first":"jonny","last":"brooks"},"observers":[{}
// ]}
model.profile = {name: {first: 'jonny', last: 'brooks'}};

// make a change to available games - no listeners are registered, so all
// it does is change the model, nothing else
model.availableGames['1234'] = {players: []};

Hope this is useful!