{"id":80,"date":"2007-04-12T21:25:49","date_gmt":"2007-04-12T19:25:49","guid":{"rendered":"http:\/\/lukav.com\/wordpress\/2007\/04\/12\/firefox-firebug-and-synchronos-calls-problem\/"},"modified":"2025-05-24T16:27:22","modified_gmt":"2025-05-24T14:27:22","slug":"firefox-firebug-and-synchronos-calls-problem","status":"publish","type":"post","link":"https:\/\/lukav.com\/wordpress\/2007\/04\/12\/firefox-firebug-and-synchronos-calls-problem","title":{"rendered":"Firefox firebug and synchronos calls problem"},"content":{"rendered":"

For those of you that have discovered that when you have Firebug <\/a>installed and are developing some synchronous XMLHttpRequest everything works, and when you disable it it stops: here is the problem.<\/p>\n

Believe it or not it is a bug in Firefox<\/a> NOT in Firebug. It turns out that Firefox<\/a> doesn’t call onreadystatechange when the you set the 3 parameter (async) to false in open. Probably FF <\/a>expects that when a call is synchronous the developer will process the result in the lines following the send call. May be this make sense, but if you want to quickly test async\/sync calls or use a library that doesn’t take care of this, you be in trouble.<\/p>\n

I can say for certain (I’ve committed the code myself) that the next release of OpenLink AJAX Toolkit<\/a> won’t have this problem and will make no difference if you have Firebug <\/a>or not.<\/p>\n

I use the following to catch the situation where Firebug <\/a>is not installed or is installed but disabled:<\/p>\n

if (OAT.Browser.isGecko)\r\n{\r\n  try {\r\n    if (!xhr.options.async && xhr.obj.onreadystatechange == null) {\r\n      OAT.AJAX.response(xhr);\r\n    }\r\n  } catch (e) {\r\n    if ((e.message && e.message == 'Permission denied to create wrapper for object of class UnnamedClass') ||\r\n         e == 'Permission denied to create wrapper for object of class UnnamedClass')\r\n      OAT.AJAX.response(xhr);\r\n }\r\n}<\/pre>\n
OAT.Dom.isGecko() – return true if it mozilla and derivatives
\nOAT.AJAX.response – is the function that is normally called when the request finish.
\nxhr.options.async – is holding if the call is async or not
\nxhr.obj.onreadystatechange – is the original Firefox XMLHttpRequest object instance, since the code above works in the context of OAT<\/a><\/p>\n