Create a Message in Discussions List

createMessage.js

function createMessage(discussionItem,properties,OnItemAdded,OnItemError)
{
    var context = new SP.ClientContext.get_current();
    var messageItem = SP.Utilities.Utility.createNewDiscussionReply(context, discussionItem);
    for(var propName in properties) {
       messageItem.set_item(propName, properties[propName]) 
    }
    messageItem.update();
    context.executeQueryAsync(
        function() {
          OnItemAdded(messageItem);           
        },
        OnItemError
    );
}

function createMessages(discussionItem,messagesProperties,OnItemsAdded,OnItemsError)
{
    var context = new SP.ClientContext.get_current();
    var messageItems = [];
    $.each(messagesProperties, function (i, properties) {
       messageItems.push(SP.Utilities.Utility.createNewDiscussionReply(context, discussionItem));
       for(var propName in properties) {
          messageItems[i].set_item(propName, properties[propName]) 
       }
       messageItems[i].update();       
    });
    
    context.executeQueryAsync(
        function() {
          OnItemsAdded(messageItems);           
        },
        OnItemsError
    );
}