To find how many checkboxes are checked, you can use something like:

var checkedNum = $('input[name=city[]]:checked').length;

if (!checkedNum) {

    // User didn't check any checkboxes

}

Since you're providing the same name attribute to all the checkboxes (from your PHP loop), you can use the selector input[name=city[]] to target and find them all. But to find out how many specifically are checked, you can add the :checked selector. An alternative to this is using $('input[name=city[]]').filter(:checked).

Finally, !checkedNum will only pass if checkedNum is 0, since 0 is falsey. Any other number is truthy, and wouldn't satisfy the condition !checkedNum.

References:

• jQuery attribute equals selector: http://api.jquery.com/attribute-equals-selector/


• :checked selector: http://api.jquery.com/checked-selector/


• jQuery .length property: http://api.jquery.com/length/