JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <input type="checkbox" id="asdf" />
    
</form>

JavaScript

function AddressBookEntryObj(user, selectField) {
    this.selectField = selectField;
    this.user = user;
    this.makingRequest = false;
    this.debugMode = false;

    Event.observe(this.selectField, 'change', handleEvent.bind(this));
}

//Prototype statements
AddressBookEntryObj.prototype.handleEvent = handleEvent;
//End prototype statements

function handleEvent(e) {
    alert(this.user); // your addressbook
    alert(e.target); // the form element
    try {
        if (!this.makingRequest) {
            this.makingRequest = true;
            var ajax =
            new Ajax.Request('/servlet/MyReallyCoolServlet', {
                method: 'get',
                parameters: {
                    action: 'doGet',
                    whichFunc: 'MyReallyCoolFunction',
                    fieldValue: $(this).getValue(),
                    user: this.user
                },
                onCreate: handleAjaxCreate,
                onComplete: handleChangeComplete
            });
            return true;
        }
        else {
            return false;
        }
    }
    catch (ex) {
        alert("handleEvent Error: \r\n" + ex.toString());
    }
}

var a = new AddressBookEntryObj('me', document.getElementById('asdf'));