Javascript for updating one windows from another

window.onload = initWindows;

function initWindows() {
if (document.getElementById("childField")) {
document.getElementById("childField").onchange = updateParent;
}
else {
newWindow = window.open("child.html","newWin","status=yes,width=300,height=300");
}
}

function updateParent() {
opener.document.getElementById("msgLine").value = "Hello " + this.value + "!";
}