Edit in JSFiddle

var actionList = document.getElementById("actionList");
actionList.onmouseover = function () { selectElementMouseover(actionList); }
actionList.onmouseleave = function () { selectElementMouseleave(actionList); }

function selectElementMouseover(element) {
    fireEvent(element, "mousedown");
    fireEvent(element, "mouseup");
}

function selectElementMouseleave(element) {
    fireEvent(element, "mousedown");
}

// To fire any event from JavaScript.
function fireEvent(node, eventName) {
    var doc;
    if (node.ownerDocument) {
        doc = node.ownerDocument;
    } else if (node.nodeType == 9) {
        doc = node;
    } else {
        throw new Error("Invalid node passed to fireEvent: " + node.id);
    }

    if (node.dispatchEvent) {
        var eventClass = "";

        // Different events have different event classes.
        switch (eventName) {
            case "click": // 'click' works correctly in Safari. For other we should use 'mousedown' or 'mouseup'.
            case "mousedown":
            case "mouseup":
                eventClass = "MouseEvents";
                break;

            case "focus":
            case "change":
            case "blur":
            case "select":
                eventClass = "HTMLEvents";
                break;

            default:
                throw "fireEvent: Couldn't find an event class for event '" + eventName + "'.";
                break;
        }
        var event = doc.createEvent(eventClass);

        var bubbles = eventName == "change" ? false : true;
        event.initEvent(eventName, bubbles, true); // All events created as bubbling and cancelable.

        event.synthetic = true; 
        node.dispatchEvent(event, true);
    } else if (node.fireEvent) {
        var event = doc.createEventObject();
        event.synthetic = true; 
        node.fireEvent("on" + eventName, event);
    }
};

<select id="actionList">
 <option action="">ACTIONS</option>
 <option action="add">ADD NEW</option>
 <option action="edit">EDIT</option>
</select>