TypeScript/JavaScript Dictionary class

I recently implemented a dictionary class in TypeScript. I'm still new to JavaScript so I'm curious what people think about it.

class Dictionary {
    public constructor ();
    public constructor (object: Object);
    public constructor (object?) {
        if (object != null) {
            for (let property in object) {
                if (object.hasOwnProperty(property)) {
                    this[property] = object[property];
                }
            }
        }
    }

    public clone(): Dictionary {
        let result = new Dictionary(this);
        return result;
    }

    public getKeys(): string[] {
        let result = [];
        for (let item in this) {
            if (this.hasOwnProperty(item)) {
                result.push(item);
            }
        }
        return result;
    }

    public getValues(): any[] {
        let result = [];
        for (let item in this) {
            if (this.hasOwnProperty(item)) {
                result.push(this[item]);
            }
        }
        return result;
    }

    public tryAddItem(key: string, value: any): boolean {
        let isAddItem = !this.hasOwnProperty(key) && typeof(value) !== 'undefined';
        if (isAddItem) {
            this[key] = value;
        }
        return isAddItem;
    }

    public tryUpdateItem(key: string, value: any): boolean {
        let isUpdateItem = this.hasOwnProperty(key) && typeof(value) !== 'undefined';
        if (isUpdateItem) {
            this[key] = value;
        }
        return isUpdateItem;
    }

    public tryDeleteItem(key: string): boolean {
        let isDeleteItem = this.hasOwnProperty(key);
        if (isDeleteItem) {
            delete this[key];
        }
        return isDeleteItem;
    }
}

I realized that objects in JavaScript act a lot like dictionaries so I'm basically just adding functionality to the object. I'm not sure how I would want to handle sorting. I think I would prefer to create a method that returned a sorted array or object based on some function. Similar to what a JavaScript Linq library would do.