Regular Expression for MM/DD/YYYY in Javascript

Question

I've just written this regular expression in javaScript however it doesn't seem to work, here's my function:

function isGoodDate(dt){
    var reGoodDate = new RegExp("/^((0?[1-9]|1[012])[- /.](0?[1-9]|[12][0-9]|3[01])[- /.](19|20)?[0-9]{2})*$/");
    return reGoodDate.test(dt);
}

and this is how I call it in my form validation

if(!isGoodDate(userInput[1].value)){
           alert("date not in correct format of MM/dd/YYYY");
           return false;  
        }

now I want it to return MM/DD/YYYY however if I put a valid date in it raises the alert? Any ideas anyone?

Answer 1

Maybe because you are declaring the isGoodDate() function, and then you are calling the isCorrectDate() function?

Try:

function isGoodDate(dt){
    var reGoodDate = /^(?:(0[1-9]|1[012])[\/.](0[1-9]|[12][0-9]|3[01])[\/.](19|20)[0-9]{2})$/;
    return reGoodDate.test(dt);
}

Works like a charm, test it here.

Notice, this regex will validate dates from 01/01/1900 through 31/12/2099. If you want to change the year boundaries, change these numbers (19|20) on the last regex block. E.g. If you want the year ranges to be from 01/01/1800 through 31/12/2099, just change it to (18|20).

Answer 2

Attention, before you copy+paste: The question contains some syntactic errors in its regex. This answer is correcting the syntax. It is not claiming to be the best regex for date/time parsing.

Try this:

function isGoodDate(dt){
    var reGoodDate = /^((0?[1-9]|1[012])[- /.](0?[1-9]|[12][0-9]|3[01])[- /.](19|20)?[0-9]{2})*$/;
    return reGoodDate.test(dt);
}

You either declare a regular expression with:

new RegExp("^((0?[1-9]|1[012])[- /.](0?[1-9]|[12][0-9]|3[01])[- /.](19|20)?[0-9]{2})*$")

Or:

/^((0?[1-9]|1[012])[- /.](0?[1-9]|[12][0-9]|3[01])[- /.](19|20)?[0-9]{2})*$/

Notice the /