Proxy API implementation example

gistfile1.js

/**
 * Proxy API implementation example
 * @link https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Proxy
 */
let proxyHandlerMaker = function(obj) {
    return {
        // Fundamental traps
        getOwnPropertyDescriptor: function(name) {
            var desc = Object.getOwnPropertyDescriptor(obj, name);
            // a trapping proxy's properties must always be configurable
            if (desc !== undefined) {
                desc.configurable = true;
            }

            return desc;
        },
        getPropertyDescriptor:  function(name) {
            var desc = Object.getPropertyDescriptor(obj, name); // not in ES5
            // a trapping proxy's properties must always be configurable
            if (desc !== undefined) {
                desc.configurable = true;
            }

            return desc;
        },
        getOwnPropertyNames: function() {
            return Object.getOwnPropertyNames(obj);
        },
        getPropertyNames: function() {
            return Object.getPropertyNames(obj);                // not in ES5
        },
        defineProperty: function(name, desc) {
            Object.defineProperty(obj, name, desc);
        },
        delete: function(name) {
            return delete obj[name];
        },
        fix: function() {
            if (Object.isFrozen(obj)) {
                return Object.getOwnPropertyNames(obj).map(function(name) {
                    return Object.getOwnPropertyDescriptor(obj, name);
                });
            }

            // As long as obj is not frozen, the proxy won't allow itself to be fixed
            return undefined; // will cause a TypeError to be thrown
        },

        // derived traps
        has: function(name) { return name in obj; },
        hasOwn: function(name) { return Object.prototype.hasOwnProperty.call(obj, name); },
        get: function(receiver, name) {
            if (name == "schemeIs") {
                return function(aScheme) {
                    aScheme = aScheme.toLowerCase();
                    return (aScheme == obj.scheme) || (aScheme == "chrome" && /\.dtd$/.test(obj.spec));
                };
            }

            return obj[name];
        },
        set: function(receiver, name, val) {
            obj[name] = val;
            return true;
        },
        enumerate:    function() {
            let result = [];
            for (name in obj) {
                result.push(name);
            };

            return result;
        },
        keys: function() { return Object.keys(obj); }
    };
};