For example, if privileged code accesses a DOM object belonging to web content, it will by default see it using Xray vision, meaning that among other things expando properties added to the object by content are not visible. Privileged code can waive Xray vision using
waiveXrays, and it will then see expandos. It can then use
unwaiveXrays to restore its Xray vision for the object.
waiveXrays operation is transitive: it waives Xrays not just for the given object, but for all properties of the object (and their properties, and so on). The
unwaiveXrays operation undoes the operation, so Xray vision is restored transitively as well.
xray = Components.utils.unwaiveXrays(obj);
- The object for which we wish to restore Xrays.
The object with Xrays restored.
Suppose a page script adds an expando to its global window:
// page script foo = "I'm an expando";
By default, chrome code won't see
foo, because it sees the content window with Xray vision, but the chrome code can waive Xray protection. The chrome code can then use
unwaiveXrays to restore Xray protection:
// chrome code // contentWindow is an Xray var isXray = Components.utils.isXrayWrapper(gBrowser.contentWindow); // true // expandos are not visible in Xrays var foo = gBrowser.contentWindow.foo; // undefined // you can waive Xray vision for an object var waived = Components.utils.waiveXrays(gBrowser.contentWindow); isXray = Components.utils.isXrayWrapper(waived); // false foo = waived.foo; // "I'm an expando" // waiving is transitive isXray = Components.utils.isXrayWrapper(waived.document); // false // use unwaiveXrays to undo the waiver var unwaived = Components.utils.unwaiveXrays(waived); isXray = Components.utils.isXrayWrapper(unwaived); // true foo = unwaived.foo; // undefined // unwaiving is transitive isXray = Components.utils.isXrayWrapper(unwaived.document); // true