validating a date in javascript

Question

This is the client script function for an asp.net validation control.

<script type="text/javascript">
    function validateDateControl(sender, args) {

        var d = new Date(args.Value);

        args.IsValid = (Object.prototype.toString.call(d) === "[object Date]");

        if (!args.IsValid) {
            sender.innerText = "Client: Invalid date";
        }     

        return args.IsValid;
    }
</script>

Immediate Window Results:
d
NaN
Object.prototype.toString.call(d) === "[object Date]"
true

Why is the comparison evaluating True?

I cannot understad your question. Please, post more details. Sorry :) — Angelo Badellino
– Angelo Badellino, Commented Feb 16, 2012 at 15:18
An invalid date is still a date object, it just can't be represented properly. — Marc B
– Marc B, Commented Feb 16, 2012 at 15:18

Matt Ball · Accepted Answer · 2012-02-16 15:16:20Z

8

Because new Date('as;dlas;ld,as;dl,as') is still a Date object.

> var d = new Date('as;dlas;ld,as;dl,as')
  undefined
> d.toString()
  "Invalid Date"
> Object.prototype.toString.call(d)
  "[object Date]"

A better way to check date validity is to see that Date.getTime() does not return NaN:

function validateDateControl(sender, args) {

    var d = new Date(args.Value);

    args.IsValid = !isNaN(d.getTime());

    if (!args.IsValid) {
        sender.innerText = "Client: Invalid date";
    }     

    return args.IsValid;
}

answered Feb 16, 2012 at 15:16

Matt Ball

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Comments

ixx · Accepted Answer · 2012-02-16 15:18:15Z

0

Because it's an object of type Date but the value (what is shown in string representation of the object itself, not the type) is invalid.

answered Feb 16, 2012 at 15:18

ixx

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