Python dict methods for JS objects

dict.js

Object.defineProperty(Object.prototype, "setdefault", {
    value: function(key, value) {
        if (!this.hasOwnProperty(key)) {
            if (typeof value === 'undefined') value = null;
            this[key] = value;
            return value;
        }
        return this[key];
    }
});

Object.defineProperty(Object.prototype, "pop", {
    value: function(key, value) {
        if (!this.hasOwnProperty(key)) {
            if (typeof value !== 'undefined') return value;
            return this[key];
        }
        value = this[key];
        delete this[key];
        return value;
    }
});