Javascript Makes Me Cry: Turning a Date into a String
Working late last night in Alva I wanted to do something that sounded trivial:
When the page loads, get the current date and time, and if a certain input is empty, put it there like this:
28/05/2013 23:45
So, how hard can that be, right? Well not hard, but...
Getting the current date-time is easy: now = new Date();
So, is there something like strftime in Javascript? Of course not. You can get code from the usual places and
have a untested, perhaps broken, limited version of it. And I am not about to add a strftime implementation to use it once.
Sure, there are a number of Date methods that convert to strings, but none of them lets you specify the output format.
So, let's try to do this The Javascript Way, right?
To get the elements I want to put in the value, I used accessor methods. So, obviously, these should give me what I want for the string, right?
now.getDay(), now.getMonth(), now.getYear(), now.getHour() now.getMinute()
Well, they are, at the date mentioned above, respectively: 2, 4, 113, error, error
Ok, the errors are easy to fix from the docs. It's actually getHours()
and getMinutes()
, so now we have 2, 4, 113, 23, 45 and of those five things, the last two are what one would expect, at least. Let's go over the other three and see why they are so weird:
-
Date.getDay()
returned 2 instead of 28 -
Because
getDay()
gives you the week day and not the day of the month. Which is absolutely idiotic. So, you have to usegetDate()
instead. Which means the name is a lie, becasue the logical thing forgetDate()
to return is the whole date. -
Date.getMonth()
returned 4 instead of 5 -
Because
getMonth()
returns months in the [0,11] range. Which is beyond idiotic and bordering in evil. Come on, Javascript, people have been referring to may as "5" for nearly two thousand years now! What other language does this? Anyone knows one? -
Date.getYear()
returned 113 instead of 2013 -
Because it uses offset-from-1900. Which is amazing, and I had never heard of a language doing in a standard type. Because why? So, use
getFullYear()
instead.
Now, armed with the right 5 numbers, let's format it. Does Javascript have the equivalent of sprintf or format ? Of course not. In JavaScript, without 3rd party modules, you create strings by addition, like a caveman. Again, I know I could add a format method to the String prototype and make this work, but I am not adding an implementation of format or sprintf just to use it once!
So, this produces that I want:
now.getDate()+'/'+(now.getMonth()+1)+'/'+now.getFullYear()+' '+now.getHours()+':'+now.getMinutes()
Unless... the day or month are lower than 10, in which case it's missing the left-padding zero. Luckily, for the purpose I was using it, it worked anyway. Because OF COURSE there's no included function to left-pad a string. You have to do it by addition. Or, of course, add a 3rd party function that's out there, in the internet, somewhere.
I kindly direct you to http://momentjs.com/
Yes, I saw it mentioned, but I am not adding this: https://raw.github.com/timr... to avoid one ugly line :-)
Mi opinión es que tenés que asumir las stdlib de javascript que implementan los browsers como lo que son: incompatibles, rotas, inútiles.
Y luego elegir para tus proyectos un par de bibliotecas buenas, como la que te sugieren acá y usar eso. Lo mismo que con CSS.
No sé si era una pregunta retórica, pero sobre otro lenguaje que sea "zero-based" para los meses, Java, en el paquete java.util.Calendar tiene ese hermoso comportamiento.
Argh? ;-)
Exactamente, era parte de la movida para que "JavaScript sea lo más parecido a Java", copiado del horrible diseño de Calendar circa 1996/1998. Y como muchas otras cosas en software, simplemente quedó así.
Your update thoughtfully does mention the origins in:
http://en.cppreference.com/...
"What other language does this? Anyone knows one?"
http://docs.oracle.com/java...
http://docs.oracle.com/java...
Is also 0-based month, 1900 based year. Perl does this too. Actually, is fairly common.
0 based month is convenient for arrays referencing month. Which was often used for, oh, localising the month string which was often the only string people had in a date.
1900 makes less sense, but common in languages from back then. Bit silly to be sure, but fairly harmless if you're aware of it.
I'd also like to note you shouldn't use getYear in JavaScript ever, since while most browsers follow the specification and do the -1900 thing, IE8 and older do not.
Oh, extra fun :-)
Thanks for the comment!
y = (new Array(count + 1 - x.toString().length)).join('0') + x;
For padding. Various other solutions listed here:
http://stackoverflow.com/qu...
Really though, I probably would just have called toLocaleFormat or toLocaleDateString- has advantage of being, oh, localised :)
And. Yes, the default JS API lacks a lot. Fortunately there are a ton of libs out there, so this is usually not a big deal.
Oh... And +1 for doing server side. No reason not to support non-JS if possible.
Ok. Done now.
Yeah, saw some of those, and I can't describe my happiness when it worked without the padding ;-)