It seems checking against null works, but is it a correct method? How can I correctly check that object is not dead? And where is the definition of dead object?

It seems checking against null works, but is it a correct method? How can I correctly check that object is not dead? And where is the definition of dead object?

• javascript
• object
• firefox-addon
• mozilla

• Can you provide some code? – Traveling Tech Guy Commented Jul 30, 2014 at 16:18

3 Answers 3

This is likely due to holding zombie partments. If you are storing a window in a variable you should use weak reference, otherwise it will keep the process alive.

Great read right here:

MDN article about Zombie partments

This is how to use weak references:

MDN documentation for Components.utils.getWeakReference

A dead object, is holding a strong (keep alive) reference to a DOM element (usually) that persists even after it was destroyed in the DOM.

Sometimes checking if it is undefined or null does not work, a trick I saw once and use sometimes is to check if parentNode exists (so not null or undefined).

If you cannot use weak references as suggested by Blagoh, then you can use Components.utils.isDeadWrapper() function to check (added in Firefox 17 but still not really documented):

if (Components.utils.isDeadWrapper(element))
  alert("I won't touch that, it's a dead object");

Unprivileged code doesn't really have a way of recognizing dead objects without triggering an exception. Then again, if an object throws an exception no matter what you do then it is probably dead:

try
{
  String(element);
}
catch (e)
{
  alert("Better not touch that, it's likely a dead object");
}

Dead object would mean an object whose parent document has been destroyed, and the references are removed to eliminate memory leaks in add-ons. So you could check for the element, as:

if( typeof some_element !== 'undefined') {
    //its not dead
}

See Dead Object Reference