addEventListener() question/weird behavior - ajax

Question

I'm developing a game for Facebook. I'm using PHP and FBJS. I'm using addEventListener() to attach events to two buttons. Each button has it's own event handler which is a js function. The first event handler (loadNewCargo()) gets called with no problems. But the second event handler (discardExistingCargo()) causes the page to refresh when it is called. The examples I've seen use a single event handler function for multiple elements. I'm creating one handler for each element. Is this illegal? Here's the code ('load-new-submit' and 'discard-existing-submit' are the IDs for the two buttons on the dialog):
function loadCargo() {
var actionPrompt = document.getElementById('action-prompt');
actionPrompt.setTextValue('Loading cargo...');
var ajax = new Ajax();
ajax.responseType = Ajax.JSON;
ajax.ondone = function(data) {
//debugger;
ajax.responseType = Ajax.FBML;
ajax.ondone = function(fbjsData) {
//debugger;
if(data.loadableCargo.length == 0) {
moveTrainManual();
} else {
var dialog = new Dialog().showChoice('Load Cargo', fbjsData, 'Minimize', 'Pass');
var dlgBtnNew = document.getElementById('load-new-submit');
dlgBtnNew.cityId = data.loadableCargo.city_id;
dlgBtnNew.trainId = data.loadableCargo.train_id;
dlgBtnNew.addEventListener('click', loadNewCargo);
/**/
var dlgBtnDiscard = document.getElementById('discard-existing-submit');
dlgBtnDiscard.cityId = data.loadableCargo.city_id;
dlgBtnDiscard.trainId = data.loadableCargo.train_id;
dlgBtnDiscard.addEventListener('click', discardExistingCargo);
/**/
dialog.onconfirm = function() {
// Submit the form if it exists, then hide the dialog.
dialog.hide();
actionPrompt = document.getElementById('action-prompt');
actionPrompt.setInnerXHTML('<span><div id="action-text">'+
'The "Load cargo" dialog has been minimized'+
'</div>'+
'<div id="action-end">'+
'<form action="" method="POST">'+
'<input type="button" value="Maximize" id="next-phase" onclick="loadCargo();" />'+
'</form>'+
'</div></span>');
actionButton = document.getElementById('next-phase');
actionButton.setValue('Maximize');
actionButton.addEventListener('click', loadCargoEventHandler);
};
dialog.oncancel = function() {
moveTrainManual();
}
}
}
ajax.post(baseURL + '/turn/load-cargo-dialog-fbjs', data);
}
ajax.post(baseURL + '/turn/load-cargo');
}
function loadCargoEventHandler(evt) {
if(evt.type == 'click') {
var dialog = new Dialog().showChoice('Load Cargo', fbjs_load_cargo_select, 'Minimize', 'Pass');
dialog.onconfirm = function() {
// Submit the form if it exists, then hide the dialog.
dialog.hide();
var actionPrompt = document.getElementById('action-prompt');
actionPrompt.setInnerXHTML('<span><div id="action-text">'+
'The "Load cargo" dialog has been minimized'+
'</div>'+
'<div id="action-end">'+
'<form action="" method="POST">'+
'<input type="button" value="Maximize" id="next-phase" onclick="loadCargo();" />'+
'</form>'+
'</div></span>');
var actionButton = document.getElementById('next-phase');
actionButton.setValue('Maximize');
actionButton.addEventListener('click', loadCargoEventHandler);
};
dialog.oncancel = function() {
moveTrainManual();
}
}
}
function loadNewCargo(evt) {
//new Dialog().showMessage('loadNewCargo', 'city id='+cityId+', train id='+trainId);
//debugger;
cityId = evt.target.cityId;
trainId = evt.target.trainId;
ajax = new Ajax();
ajax.responseType = Ajax.JSON;
param = { 'load-cargo-submit': "Load new goods", 'city-id': cityId, 'train-id': trainId };
ajax.ondone = function(data) {
openCargoHolds = data.openCargoHolds;
cargoHoldsUsed = 0;
ajax.responseType = Ajax.FBML;
param = { 'openCargoHolds': data.openCargoHolds, 'cityGoods': data.cityGoods, 'trainId': data.trainId };
ajax.ondone = function(fbjsData) {
//debugger;
var dialog = new Dialog().showChoice('Load Cargo', fbjsData, 'Load cargo', 'Cancel');
dialog.onconfirm = function() {
var goods = [];
var goodsIds = [];
numGoods = document.getElementById('goods-count').getValue();
for(var i = 0; i < numGoods; i++) {
j = i + 1;
goods[i] = document.getElementById('goods-' + j).getValue();
goodsIds[i] = document.getElementById('goods-id-' + j).getValue();
}
var trainId = document.getElementById('train-id').getValue();
param = { "goods": goods, "goods-id": goodsIds, "train-id": trainId };
ajax.responseType = Ajax.JSON;
ajax.ondone = function(data) {
loadCargo();
}
ajax.post(baseURL + '/turn/do-load-cargo-new', param);
//dialog.hide();
};
dialog.oncancel = function() {
loadCargo();
}
}
ajax.post(baseURL + '/turn/load-cargo-new-dialog-fbjs', param);
}
ajax.post(baseURL + '/turn/load-cargo-select', param);
}
function discardExistingCargo(evt) {
//new Dialog().showMessage('loadNewCargo', 'city id='+cityId+', train id='+trainId);
cityId = evt.target.cityId;
trainId = evt.target.trainId;
/**/
ajax = new Ajax();
ajax.responseType = Ajax.JSON;
param = { 'load-cargo-submit': "Discard existing goods", 'city-id': cityId, 'train-id': trainId };
ajax.ondone = function(data) {
ajax.responseType = Ajax.FBML;
param = { 'openCargoHolds': data.openCargoHolds, 'trainGoods': data.trainGoods, 'trainId': data.trainId };
ajax.ondone = function(fbjsData) {
var dialog = new Dialog().showChoice('Discard Cargo', fbjsData, 'Discard cargo', 'Cancel');
dialog.onconfirm = function() {
var goods = [];
var goodsIds = [];
numGoods = document.getElementById('goods-count').getValue();
for(var i = 0; i < numGoods; i++) {
j = i + 1;
goods[i] = document.getElementById('goods-' + j).getValue();
goodsIds[i] = document.getElementById('goods-id-' + j).getValue();
}
var trainId = document.getElementById('train-id').getValue();
param = { "goods": goods, "goods-id": goodsIds, "train-id": trainId };
ajax.responseType = Ajax.JSON;
ajax.ondone = function(data) {
loadCargo();
}
ajax.post(baseURL + '/turn/do-load-cargo-discard', param);
//dialog.hide();
};
dialog.oncancel = function() {
loadCargo();
}
}
ajax.post(baseURL + '/turn/load-cargo-discard-dialog-fbjs', param);
}
ajax.post(baseURL + '/turn/load-cargo-select', param);
/**/
}
Thank you for any assistance you can offer.

Answer 1

You can return false; from the discardExistingCargo function to avoid the default submit action - which is causing the page to refresh.

Answer 2

Problem solved: the button's input type was "submit", hence the page refresh (doh!)