function getPermissions()
{
    var mycontext = new SP.ClientContext();
    var mysite = mycontext.get_web();
    var mylist = mysite.get_lists().getByTitle(‘Demo‘);
    myitem = mylist.getItemById(16);

    mycontext.load(myitem,‘EffectiveBasePermissions‘);
    mycontext.executeQueryAsync(function(){
        var perms = myitem.get_effectiveBasePermissions();
        if (perms.has(SP.PermissionKind.editListItems)) {
            alert("Yes!");
        }
        else
        {
            alert("No!");
        }
    },function(){});
}

SP.SOD.executeFunc(‘sp.js‘,‘SP.ClientContext‘,getPermissions);