Error creating Date() in Javascript

Question

I'm totally new to Javascript, and I'm getting trouble creating a Date from milliseconds.

I have this code:

function (result) {

  alert("Retreived millis = " + result.created);
  //Prints "Retrieved millis = 1362927649000"

  var date = new Date(result.created);
  alert("Created Date = " + date);
  //Prints "Created Date = Invalid Date"

  var current = new Date();
  var currentDate = new Date(current.getTime());
  alert("Current Date = " + currentDate);
  //Prints "Current Date = Sun Apr 14 2013 12:56:51 GMT+0100"
}

The last alert proves that the creation of Date is working, but I don't understand why the first Date is not being created correctly, because the retrieved millis are correct... and as far as I understand in Javascript there're not datatypes, so it can't fail because the retrieved millis are a string or a long, right?

T.J. Crowder · Accepted Answer · 2013-04-14 12:04:50Z

2

I suspect result.created is a string. Since the Date constructor accepts strings but expects them to be in a different format than that, it fails. (E.g., new Date("1362927649000") results in an invalid date, but new Date(1362927649000) gives us Sun Mar 10 2013 15:00:49 GMT+0000 (GMT).)

This should sort it (by converting to a number first, so the constructor knows it's dealing with milliseconds since The Epoch):

var date = new Date(parseInt(result.created, 10));

answered Apr 14, 2013 at 12:04

T.J. Crowder

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3 Comments

MikO Over a year ago

It solved the problem. I thought that Javascript wouldn't complain if you pass a integer or a string... As said I'm totally new to this... Thanx a lot!

T.J. Crowder Over a year ago

@MikO: JavaScript will do a lot of automatic string-to-number conversions, but it just happens that the Date constructor accepts either a string or a number, and so it doesn't trigger the automatic conversion. Instead, it looks at what it has and branches, either parsing a string in a given format, or using the number. If a function only allows numbers, odds are high it'll happily auto-convert the string for you (Math.max(10, "100") returns 100, for instance). Just not the Date constructor. :-)

MikO Over a year ago

OK, I clearly understand it now. Thanx very much for the solution and for the extra info.

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