JavaScript function to check date format [compare all]

//Text box for date name = "indate"
function check1(Form)
{
for (i = 0; i < ; i++)
{
if ([i].value == "")
{
alert("Please fill in the complete!")
[i].focus();
return;
}

if ([i].name == "indate")
{
var date = [i].value;
len = ;
var datearray = ("-")
//alert(datearray[1]);
var year = parseInt(datearray[0]);
var month = parseInt(datearray[1]);
var day = parseInt(datearray[2]);

if (len == "")
{
alert("Time cannot be empty");
return;
}
else if (len > 10)
{
alert("Date format is incorrect");
return;
}
else if (isNaN(year))
{
alert("Date format is incorrect");
return;
}
else if ((year > 9999) || (year < 100))
{
alert("Date format is incorrect");
return;
}
else if (isNaN(month))
{
alert("Date format is incorrect");
return;
}
else if ((month > 12) || (month < 1))
{
alert("Date format is incorrect");
return;
}
else if (isNaN(day))
{
alert("Date format is incorrect");
return;
}
else
{
switch (month)
{
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
if ((dat < 0) || (day > 31))
{
alert("Date format is incorrect");
return;
}
break;
case 4:
case 6:
case 9:
case 11:
if ((day < 0) || (day > 30))
{
alert("Date format is incorrect");
return;
}
break;
default:
if ((year % 100 == 0) && (year % 4 == 0))
{
if ((day < 0) || (day > 29))
{
alert("Date format is incorrect");
return;
}
}
else
{
if ((day < 0) || (day > 28))
{
alert("Date format is incorrect");
return;
}
}
}
}
}
}
();
}