How to disable the rich text control in share using JS

I was trying with read-only="true" to disable the rich text control for meta data in share-config-custom.xml. But unfortunately it does not work for me. So I tried with the following code snippet to disable the cm:description field.

 var lookupObject = Alfresco.util.ComponentManager.find({name : "Alfresco.FormUI"});
 var me = lookupObject[0];
        var tinyInstance = Dom.get(me.parentId+'_prop_cm_description_ifr');
        var tinyToolBar = Dom.get(me.parentId+'_prop_cm_description_toolbargroup');
        tinyInstance.contentDocument.body.contentEditable = false;
        tinyToolBar.hidden = "true";