Getting Error "Setting a property that has only a getter" in java script

function OpenModalWindow(url,name){
    if(name===undefined){
        window.open(url,"_blank","status=0,toolbar=0,menubar=0,resizable=1,scrollbars=1");
    }
    else{
        window.open(url,name,"status=0,toolbar=0,menubar=0,resizable=1,scrollbars=1");
    }
    return false;
}