Get list items using ECMA script

<script type="text/javascript">
    ExecuteOrDelayUntilScriptLoaded(retrieveMarketingPromotions, "sp.js");
    function retrieveMarketingPromotions() {

        var clientContext = SP.ClientContext.get_current();
        var oList = clientContext.get_web().get_lists().getByTitle('Marketing Promotions');

        var camlQuery = new SP.CamlQuery();
        camlQuery.set_viewXml('<View><Query><OrderBy><FieldRef Name="Modified" Ascending="False" /></OrderBy></Query><RowLimit>4</RowLimit></View>');
        this.collListItem = oList.getItems(camlQuery);
        clientContext.load(collListItem, 'Include(Title, FileRef, ID,Modified)');
        clientContext.executeQueryAsync(Function.createDelegate(this, this.onQuerySucceededMP), Function.createDelegate(this, this.onQueryFailedMP));
    }
    function onQuerySucceededMP(sender, args) {

        var listItemEnumerator = collListItem.getEnumerator();

        while (listItemEnumerator.moveNext()) {
            var oListItem = listItemEnumerator.get_current();
            var dispTitle = oListItem.get_item("Title");
            var dispUrl = oListItem.get_item("FileRef");
            var dispLI = document.createElement("li");
            var dispA = document.createElement("a");
            dispA.setAttribute("href", dispUrl);
            dispA.setAttribute("id", dispTitle);
            dispA.innerHTML = dispTitle;
            dispLI.appendChild(dispA);
            document.getElementById("lstMarketing").appendChild(dispLI);
        }
        DisplayCount();
    }

    function onQueryFailedMP(sender, args) {

        alert('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
    }
</script>

<div id="WebpartGreyBgColor">
  <div class="MarketingImage">
    <img class="image" src="/Style%20Library/Images/img_marketing.jpg" title="Marketing"/>
  </div>
  <div class="MarketingContent">
    <ul id="lstMarketing">
    </ul>
  </div>
  <div class="breakspacer">&nbsp;</div>
  <div class="viewall">
    <p>
    <a href="/Lists/MarketingPromotions/AllItems.aspx">View All</a></p>
  </div>
</div>