TypeScript like JavaScript enumerators

enumerator.js

var Enum = (function () {
    function Enum() {
        var args;
        if (!(this instanceof Enum)) {
            throw Error('Always use Enum constructor with new keyword.');
        }
        args = this.getArgs(arguments);
        if (args.some(function (arg) { return typeof arg !== 'string'; })) {
            throw TypeError('All Enum arguments have to be strings.');
        }
        args.forEach(this.setValue, this);
        this.initialArgs = args;
        Object.freeze(this);
    }
    Enum.indexingBase = 1;
    Enum.prototype.setValue = function (arg, index) {
        this[this[arg] = index + Enum.indexingBase] = arg;
    };
    Enum.prototype.getArgs = function (argumentsPseudoArray) {
        return Array.prototype.map.call(argumentsPseudoArray, function (arg) {
            return arg;
        });
    };
    Enum.prototype.toString = function () {
        return 'Enum { ' + this.initialArgs.join(', ') + ' }';
    };
    return Enum;
}());

var MyEnum = new Enum('Pending', 'InProgress', 'Submitted', 'Approved');

MyEnum.Pending              // 1
MyEnum.Approved             // 4
MyEnum[2]                   // "InProgress"
MyEnum[MyEnum.InProgress]   // "InProgress"
MyEnum.toString()           // "Enum { Pending, InProgress, Submitted, Approved }"