Check empty field from html array in javascript

Question

I have a simple HTML files with book seats field as array , the code below

<input type="checkbox" name="book[]" value="<?php echo $i; ?> /><?php echo $i; ?>

<input type="submit" value="BOOK" onclick = "checkIfSeatEmpty()" />

The javascript I used to validate if the field book is empty is:

var x=document.forms["bkfrm"].getElementById("chkbx").value;

 //alert(x);   alerts 'undefined' !
// var x=document.forms["bkfrm"].getElementById("book").length;
    alert(x);
    if (x==null || x=="")
    {
        alert("First name must be filled out");
        return false;
    }
return TRUE;

But the above code alerts as undefined ! How can I check if the field is empty?

Answer 1

try like following

var x=document.forms["bkfrm"].getElementById("book").checked;

Answer 2

there is no such id as chkbx or book in your html code.. use the following code

Jquery

$("input[name='book']:checked").val();