Simple regular expression test

[spm6]

Hi. My problem is something that I am sure almost everyone here knows.
Here we go:
I want to check the regular expression. I have this form:

<form name="registrace" method="post" action="<?php echo $_SERVER['PHP_SELF'] ?>" onSubmit="return check(registrace);">

Inside this form I have this input that represents year of born

<input type="text" id="year" name="year" value='<?php if (isset($year)) { echo $year;}?>'></td>

And now I want to check if user entered 4 numbers, i use javascript function:

function check(form){
var patt1=new RegExp(/(\d{4})/gm);
if(patt1.test(form.year.value) ){
/*this should return true when regular expression from form matches the pattern. but the condition - not working*/
/*do nothing*/
}
else{
document.getElementById('yearDiv').innerHTML = "Year of born must be four numbers. !!!";
form.year.focus();
return false;
}
}

I need to figure out this condition that will work. I don't know how to say to javascript, that he write to the yearDiv when regular expression check fails.
Any help would be appreciated.

[007Julien]

document.forms["registrace"].year.value;
or 
document.forms[0].year.value;
or 
document.registrace.year.value;

But not form.year.value

[spm6]

thanks,

you right but "form" is actually argument of the check function and i give it the value "registrace" trough submitting form - onSubmit="return check(registrace)"

so you suggest to type:
document.form.year.value in condition if(patt1.test(document.form.year.value) ){

bad news. the condition still not work

[007Julien]

Ok. I have not seen the argument nor the syntax for patt1

var patt1=/(\d){4}/gm;
// or 
var patt1=new RegExp("(\d{4})","gm");
// but not 
var patt1=new RegExp(/(\d{4})/gm);