Edit in JSFiddle

//Testing custom Exceptions - see below:
$('#submitForm').submit(function(event) {
    try {
        myFunction($('#dayOfWeek').val());
    } catch(e) {
        if(e instanceof ValidationException) {
            alert('ValidationException: ' + e.message);
        } else if(e instanceof LogicException) {
            alert('LogicException: ' + e.message);
        } else {
            alert('Other exception: ' + e.message);
        }
        /* On the other hand, this does not work(code above is valid):
        switch(e) {
            case ValidationException:
                alert('ValidationException: ' + e.message);
            break;
            case LogicException:
                alert('LogicException: ' + e.message);
            break;
            default:
                alert('Other exception: ' + e.message);
            break;
        }
        */
    }
    event.preventDefault();
});

//Define a custom exception that we would like to throw under the right conditions:
function ValidationException(number, exception) {
    this.message = exception;
    this.name = "myLibrary Validation Exception";
    this.number = number;
    this.type = "ValidationException";
}
//Possible to let our error message inherit from the general Error object:
//ValidationException.protoType = Error.protoType;
function LogicExcpetion(number, message) {
    this.message = message;
    this.name = "myLibrary Logic Exception";
    this.number = number;
    this.type = "LogicExpetion";
}
function myFunction(dayOfWeek) {
    if(dayOfWeek > 7) {
        throw new ValidationException(123, "dayOfWeek must be 7 ot less");
    }
}
<form id="submitForm" action="demo_form_action.asp" method="post">
    <b>Email:</b> <input type="text" id="dayOfWeek" value="12" /><br/>
    <input type="submit" />
</form>