新的Date（）何时在我的函数中运行？

Question

I'm still fairly new to Node and Javascript and just want to check what's going on here but I'm not sure what to even look for.

I've created a couple of functions for comparing dates...

exports.isDateWithinRange = date => (from, to) => from <= date && date <= to;
exports.isCurrentDateInRange = isDateWithinRange(new Date());

These work (for now) but I just want to check.

In the second line... when is that new Date() calculated?

• Is it calculated every time the function isCurrentDateInRange called?
• Or is it calculated once when loading the file for the first time?

Because if it's the latter I need to change it. But I didn't want to bother changing it if it's not a problem.

Thanks

Answer 1

The Date object is constructed whenever you require the module. And the isCurrentDateInRange will be the result of the immediate invocation of isDateWithinRange .

To avoid it you can use the exported isDateWithinRange and you can set default date value like this:

exports.isDateWithinRange = (date = new Date()) => (from, to) => from <= date && date <= to;