propertyDecorator.js

var __decorate = this.__decorate || function (decorators, target, key, desc) {
    if (typeof Reflect === "object" && typeof Reflect.decorate === "function") return Reflect.decorate(decorators, target, key, desc);
    switch (arguments.length) {
        case 2: return decorators.reduceRight(function(o, d) { return (d && d(o)) || o; }, target);
        case 3: return decorators.reduceRight(function(o, d) { return (d && d(target, key)), void 0; }, void 0);
        case 4: return decorators.reduceRight(function(o, d) { return (d && d(target, key, o)) || o; }, desc);
    }
};
function enumerable(enumerable) {
    if (enumerable === void 0) { enumerable = true; }
    return function (target, propertyKey) {
        Object.defineProperty(target, propertyKey, {
            configurable: true,
            writable: true,
            enumerable: false
        });
    };
}
var MyClass = (function () {
    function MyClass() {
        this.property = 'initial value';
    }
    __decorate([
        enumerable(false)
    ], MyClass.prototype, "property");
    return MyClass;
})();
var mc = new MyClass();
for (var key in mc) {
    console.log(key);
}

propertyDecorator.ts

function enumerable(enumerable: boolean = true): PropertyDecorator {
	return function (target: Object, propertyKey: string): void {
		Object.defineProperty(target, propertyKey, {
			configurable: true,
			writable: true,
			enumerable: false
		});
	};
}

class MyClass {
	@enumerable(false)
	property: string = 'initial value';
}

var mc = new MyClass();
for (var key in mc) {
	console.log(key);
}