In some of our code, we are using Number.isNaN. For example, https://github.com/Microsoft/BotFramework-WebChat/blob/master/packages/component/src/Localization/en-US.js#L12.

I think Number.isNaN is unnecessary in this case because the argument is always a number, so the result is same as global.isNaN. And second, IE11 does not support Number.isNaN.

Another change would be date.valueOf(). According to MDN, this is equivalent to date.getTime(). So I would recommend using date.getTime() for consistency.