Javascript method to ensure that a date is valid

Question

I'm trying to write a method that checks whether a date is valid. It is passed in three Strings: month, day, and year, in order. Month should be from 0-11 instead of 1-12. I have tested the logic of the code in Java and it works. is_int is another method that tests if a String is composed solely of numerical characters. Unfortunately, I am running into problems which I can't figure out.

function is_int(value) {
   for (i = 0 ; i < value.length ; i++) {
      if ((value.charAt(i) < '0') || (value.charAt(i) > '9')) return false
    }
   return true;
}

function isValidDate(value1:String, value2:String, value3:String)
{
  if (!is_int(value3)) return false;
  if (!is_int(value2)) return false;
  if (!is_int(value1)) return false;
  var v1 = parseInt(value1) + 1;
  var v2 = parseInt(value2);
  var v3 = parseInt(value3);
  if (v1 > 12 || v1 < 1) return false;
  if (v2 > 31 || v2 < 1) return false;
  if (v2 == 31) if (v1 == 2 || v1 == 4 || v1 == 6 || v1 == 9 || v1 == 11) return false;
  if (v1 != 2) return true;
  if (v2 < 29) return true;
  if (v2 == 30) return false;
  if (v3 % 400 == 0)
        return true;
  else if (v3 % 100 == 0)
        return false;
  else if (v3 % 4 == 0)
        return true;
  else
        return false; 
}

My first tester is something that asks for three text inputs and, if the isValidDate function returns false, displays an alert. If not, it forwards to a blank html page. However, I tried this:

function validate() {
  if (!isValidDate("a", "a", "a")) {
  alert("wrong");
  return false;
  }
}

and the alert never displayed and it forwarded every time. Strangely enough, this still happened when I removed the exclamation point in front of isValidDate. I also tried swapping the double quotation marks for single, but that didn't fix the problem either. The same thing happens with my tester for is_int. I have no idea where I'm going wrong.

You can use the built-in function [`isNaN`](https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/isNaN) to check whether strings are valid numbers. See http://stackoverflow.com/questions/175739/is-there-a-built-in-way-in-javascript-to-check-if-a-string-is-a-valid-number/175787#175787 — Jon Gauthier, Aug 05 '11 at 00:54
isNaN is a little different from my function. For example, isNaN("") returns false because "" is equal to 0 according to that function. I don't want "" to be a number so I used mine instead. — joseph, Aug 05 '11 at 01:06

OverZealous · Accepted Answer · 2011-08-05T01:23:18.657

2

I know you didn't ask for it, but here's a much more valid way to check for dates, and it handles odd dates more consistently:

function isValidDate(year, month, day) {
    var d = new Date(parseInt(year,10), parseInt(month, 10)-1, parseInt(day, 10), 0, 0, 0);
    return d.getFullYear() == year &&
           (d.getMonth()+1) == month &&
           d.getDate() == day;
}

isValidDate("2011", "08", "04"); // true
isValidDate("bob", "08", "04"); // false
isValidDate("1979", "1", "1"); // true

Fiddle with it: http://jsfiddle.net/2WJCv/

Alternate HTML-only link: http://pastehtml.com/view/b2se2lk9k.html

edited Aug 05 '11 at 01:23

answered Aug 05 '11 at 00:56

OverZealous

39,252
15
98
100

jsfiddle isn't working for me (weird proxy problem in my connection) so I can't try your example out (and am too lazy to try it locally), but does it handle non-numeric values? What does `parseInt(month,10)-1` do if month is "test"? – nnnnnn Aug 05 '11 at 01:19
parseInt(val,10) attempts to convert a string to a number. If that string is invalid, it returns `NaN`. The `-1` is because the `Date` constructor requires 0-based months. Hang on, I'll get you another link to try. (Edit, oops, meant NaN.) – OverZealous Aug 05 '11 at 01:22
+1 as this is a good method—only need to test 2 out of 3 conditions at the end though. The extra one doesn't hurt, it's just redundant. Also no need to set the hours, minutes and seconds, but again, doesn't hurt. – RobG Aug 05 '11 at 01:27
@OverZealous - yeah, I know `parseInt` can return `NaN`, and I know about the 0-based months (I don't understand _why_ they're 0-based, but I know about it). What I was really asking is what is the value of `NaN - 1`, and what happens when you pass that value to the `Date` constructor? Thanks for taking the trouble with the other link. – nnnnnn Aug 05 '11 at 02:05
`NaN +/- anything` is still `NaN` It's a bizarro special construct in JS. Luckily, passing NaN to the Date constructor just returns an "invalid date", where each date part is `NaN`. Also luckily, `NaN` does not equal anything, so the test still works. – OverZealous Aug 05 '11 at 02:07
@nnnnnn - zero based months because javascript copied Java's date object (and defects, e.g. getYear returning two digit year) so that's what it has. – RobG Aug 07 '11 at 04:03

score 0 · Answer 2 · answered Aug 05 '11 at 00:51

0

I think your problem is in the isValidDate() function: Should be function isValidDate(value1, value2, value3) I got an alert using that. Hope that helps! :)

answered Aug 05 '11 at 00:51

bozdoz

12,550
7
67
96

i.e. lose the ":String" at the end of the variables – bozdoz Aug 05 '11 at 00:51
Yup, I guess that was my only problem, even though I thought it was actually a solution to the problem. – joseph Aug 07 '11 at 01:11

jfriend00 · Answer 3 · 2011-08-05T01:42:55.050

0

If you take the illegal javascript out, it seems to work for me in this jsFiddle: http://jsfiddle.net/jfriend00/ae9aC/.

In your code, I changed this:

function isValidDate(value1:String, value2:String, value3:String)

to this:

function isValidDate(value1, value2, value3)

And, the jsFiddle alerts false when passed isValidDate("a", "a", "a").

FYI, there are a lot of ways this function could be improved. To start with, I would suggest that you change value1, value2 and value3 to month, day, year and similarly v1, v2 and v3 so the function is a lot more self describing.

Also, parseInt() should always be passed the radix parseInt(str, 10) otherwise it will "guess" the radix based on the contents of the string.

edited Aug 05 '11 at 01:42

answered Aug 05 '11 at 00:54

jfriend00

683,504
96
985
979

I didn't think type annotations were standard yet. – Ken Wayne VanderLinde Aug 05 '11 at 00:55
Thanks for your help, especially for the parseInt() tip. – joseph Aug 07 '11 at 01:10
@joseph - You could vote up the answers you found helpful. That is one of the ideas behind StackOverflow. – jfriend00 Aug 07 '11 at 01:45

score 0 · Answer 4 · answered Aug 05 '11 at 00:54

Your function declaration is invalid:

function isValidDate(value1:String, value2:String, value3:String) {
  // your code here
}

JavaScript function parameters and variable declarations don't have types, so you need to say:

function isValidDate(value1, value2, value3) {
  // your code here
}

(An unrelated suggestion: name your parameters and variables more meaningfully. If you expect month, day, year, why not call them that? Especially when dealing with dates where a lot of countries normally say day, month, year rather than month, day, year.

Another unrelated suggestion: look into regular expressions.)

Thanks this was a good answer too. I inserted the :String after the variables after doing a cursory Google search to figure out why my method didn't work before. I must have changed something else in between so when my method body finally was correct it still wouldn't run, but I didn't remember changing anything else so I got really confused. — joseph, Aug 07 '11 at 01:09

score 0 · Answer 5 · answered Aug 05 '11 at 03:21

0

If you like doing it long hand and without using the Date constructor, try:

function validDate(y, m, d) {
  // Days in month
  var days = [,31,28,31,30,31,30,31,31,30,31,30,31];
  // Adjust February it's a leap year
  if (m == 2 && (!(y%4) && y%100) || !(y%400)) {
    days[2] = 29;
  }
  // Check date in month
  return d <= days[+m];
}

It may be faster, or not. :-)

answered Aug 05 '11 at 03:21

RobG

142,382
31
172
209

I just didn't know about the Date constructor. Thanks for your answer though. – joseph Aug 07 '11 at 01:09

Javascript method to ensure that a date is valid

5 Answers5

Linked