Javascript：最短日期始终小于任何其他日期

Question

I want to compare strings that are dates

if (user_date < date)

date has yyyy-mm-dd format, so it is OK to compare dates as strings, if the user enters a valid user_date in this format.

Unfortunately, user_date is entered by the user, so it could be invalid. In case if it is invalid (or left empty), I want (user_date < date) always to be true.

I have found to set var user_date=''; if user's date is invalid. Is that a good way to make make (user_date < date) for any valid date?

The same question is for (user_date > date) (more than any date). I've found to set var user_date='A';

I need it for

if (date1 <= date && date2>= date)
//do something

So it works without any additional if then .

PS I don't want to enter var user_date='2222-12-31'; because the algorythm will stop working properly in less than 210 years.

Answer 1

为什么不将最小值设置为0000-01-01，将最大值设置为9999-12-31？

Answer 2

I think that is not possible. But what is possible is to get a date for which a comparison is always false — so functionally it behaves the same as NaN does for numbers. So if you invert the test, thus replace (a <= b) with !(a > b) , it would work.

$date = new Date(NaN);
if (!($date1 > $date) && !($date2 < $date))  ...

ps What's with the dollar signs? Are you confusing Javascript with PHP or Perl? :)

Answer 3

I think you can do somethin glike

var date = '2013-03-12';
var $date = new Date(date);
function onChange(el){
    var user_date = el.value;
    var udate = new Date(user_date);
    if(isNaN(udate.getTime()) || udate < $date){
        alert('less')
    }

}

Demo: Fiddle

Answer 4

Personally I would first validate the date that the user is entering - don't leave it to chance.

I use my own date extensions library here for this kind of stuff:

DP_DateExtensions

The parseFormat() method will let you easily validate your input. Something like this so do well:

Date.parseFormat(InputString, "YYYY-M-D")

The function returns a valid JavaScript date if the entered string matches the format or null if it doesn't. You obviously don't have to send a user message based on this if you have a default behavior you'd like to apply - but the code itself should "know".

In this case - if you want an invalid date to be less than another, known good date, then there are many ways to do it. Most simple is something like this:

InputDate = Date.parseFormat(InputString, "YYYY-M-D");
if ( InputDate || InputDate < GoodDate ) {
     Input Date is Invalid or Falls before good date
} else {
     Input Date is Falls after good date
};

You don't need to set "false dates" or guess with the right validation and Boolean logic in play and it will work until the world stops spinning (in theory).

You can you use the compare() method in the library to do any kind of greater/less than comparison to any precision.

Hope this helps.