It happens so many times that I need to code something to make the UI fool proof. While I have the logic clear in my mind, i often find that javascript is of little or no help at all.... Whats amazing is that 99% of the time jquery does the trick with minimum code and the 'why-didnt-i-look-up-the-docs-first' feeling strikes!!

Jquery can be used as follows to check if at least one checkbox (any input field actually) from a number of checkboxes is selected before submitting the form on the client side. I came across this when I was trying to figure out a way for similar validation when the number of check boxes was driven by the database and it was not possible to have a common className for them.

function validateCheckbox() {
    var n = $("input:checked").length;
    if(n == 0) {
        return false;
    } else {
        return true;
    }
}

input:checked matches all the check boxes which are checked.