<script language="ecmascript" type="text/ecmascript">
var clientContext = null;
var oWeb = null;
var oListColl = null;
var oList = null;
var oListItem = null;
var listItemCreationInfo = null;
function createListItem() {
clientContext = new SP.ClientContext.get_current();
oWeb = clientContext.get_web();
oListColl = oWeb.get_lists();
oList = oListColl.getByTitle('Custom List');
listItemCreationInfo = new SP.ListItemCreationInformation();
oListItem = oList.addItem(listItemCreationInfo);
oListItem.set_item('Title', 'New Item');
oListItem.update();
clientContext.load(oListItem);
clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceeded), Function.createDelegate(this, this.onQueryFailed));
}
function onQuerySucceeded() {
alert(oListItem.get_title() + ' item is created successfully.');
}
function onQueryFailed(sender, args) {
alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}
</script>
<input id="btnCreateListItem" onclick="createListItem()" type="button" value="Create List Item"/>