Best way to compare dates for most recent in JS?

Question

I'm talking about ones encoded in the format in which the twitter API returns its dates, like...

"Tue Jan 12 21:33:28 +0000 2010"

The best thing I thought of was to try to slice it up with regexes to become something more like...

20100112213328,

but there's got to be a better way.

I've noticed [this](http://stackoverflow.com/questions/11346741/problems-parsing-date-like-twitter) although it isn't exactly what I want. — wwaawaw, Nov 08 '12 at 08:32

score 1 · Answer 1 · answered Nov 08 '12 at 08:36

1

You can just make a new Date object using a string like "Tue Jan 12 21:33:28 +0000 2010".

var dateString = "Tue Jan 12 21:33:28 +0000 2010";
var twitterDate = new Date(dateString);

Then, you can simply use < and > to make comparisons.

var now = new Date();
if (now < twitterDate) {
    // the date is in the future
}

answered Nov 08 '12 at 08:36

evan

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woah!! Is it specified anywhere how those work? Or is it "specifically unspecified," like `localeCompare()`? – wwaawaw Nov 08 '12 at 08:37
I found this with a little googling: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Date What specifically did you want to know? – evan Nov 08 '12 at 08:39
/me heads off to read it, waiting to be able to accept yr answer. – wwaawaw Nov 08 '12 at 08:39
1

@adlwalrus: The JS date object can be tricky at first [but here's some more details on the matter](http://stackoverflow.com/questions/12007379/what-makes-new-date-1000-a-valid-javascript/12007624#12007624), though I have to make a couple edits to be 100% accurate) – Elias Van Ootegem Nov 08 '12 at 08:41
@evan doesn't seem to mention the comparison operators. – wwaawaw Nov 08 '12 at 08:46
Not sure what you mean, are you asking about < and > ? – evan Nov 08 '12 at 08:50
@adlwalrus: not directly, I've edited it just now, so that it does, but it basically deals with how JS deals with a date object in comparisons, and arithmic operations. more specifically: in combination with the overloaded `+` operator (addition and string concatenation) and the equality operators. All of that stuff _and_ how the Date objects differ from other objects – Elias Van Ootegem Nov 08 '12 at 08:50
@EliasVanOotegem, that was a great link! Tha nks. – wwaawaw Nov 08 '12 at 08:51
See also: http://stackoverflow.com/questions/13285441/how-does-js-date-comparison-work/ – wwaawaw Nov 09 '12 at 04:17

score 1 · Accepted Answer · edited Nov 08 '12 at 08:55

1

JavaScript Date will correctly parse the Twitter date :

  var d1 = new Date ("Tue Jan 12 21:33:28 +0000 2010")
    , d2 = new Date ("Tue Jan 12 22:33:28 +0000 2010");

The you can compare these using the getTime method which converts to numeric form:

  if (d1.getTime() < d2.getTime())
  {
       //...
  }

Or, simply

if (d1 < d2)
{
}

If needs must, explicitly coerce to number:

if (+(d1) < +(d2))
{
}

edited Nov 08 '12 at 08:55

Elias Van Ootegem

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answered Nov 08 '12 at 08:41

HBP

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the `>`, `<`, `>=` and `<=` operators automatically coerce a Date object to numbers, as does `+(dateObject)`... your `if` statement is incorrect BTW: you're missing a closing `)`, and it'll always return true if d1 != 0: – Elias Van Ootegem Nov 08 '12 at 08:52

score 0 · Answer 3 · answered Nov 08 '12 at 08:56

As far as the ECMAScript specification 5.1 goes (see 15.9.1.15), the only supported string interchange format for date-times is YYYY-MM-DDTHH:mm:ss.sssZ (along with shorter forms).

Otherwise (15.9.4.2):

If the String does not conform to that format the function may fall back to any implementation-specific heuristics or implementation-specific date formats.

I would use the regular expression based solution which is short and guaranteed to work anywhere; relying on the user's browser and localization parameters seems a little eerie to me.

Best way to compare dates for most recent in JS?

3 Answers3