typescript function for object deep copy

deepcopy.ts

  deepCopy(obj) {
        let copy;

        // Handle the 3 simple types, and null or undefined
        if (null == obj || "object" != typeof obj) return obj;

        // Handle Date
        if (obj instanceof Date) {
            copy = new Date();
            copy.setTime(obj.getTime());
            return copy;
        }

        // Handle Array
        if (obj instanceof Array) {
            copy = [];
            for (let i = 0, len = obj.length; i < len; i++) {
                copy[i] = this.deepCopy(obj[i]);
            }
            return copy;
        }

        // Handle Object
        if (obj instanceof Object) {
            copy = {};
            for (const attr in obj) {
                if (obj.hasOwnProperty(attr)) { copy[attr] = this.deepCopy(obj[attr]); }
            }
            return copy;
        }

        throw new Error("Unable to copy obj! Its type isn't supported.");
    }