On the standards track: Yes
Is Experimental: No
Is Deprecated: No
In Chrome version 1 on 2008-12-11
In Chrome Android version 18 on 2012-06-27
In Edge version 12 on 2015-07-29
In Firefox version 1 on 2004-11-09 Note: Starting in Firefox 30, synchronous requests on the main thread have been deprecated due to their negative impact on performance and the user experience. Therefore, the async parameter may not be false except in a Worker.
In Firefox for Android version 4 on 2011-03-29 Note: Starting in Firefox for Android 30, synchronous requests on the main thread have been deprecated due to their negative impact on performance and the user experience. Therefore, the async parameter may not be false except in a Worker.
In Internet Explorer version 5 on 1999-03-18
In Quest Browser version 5.0 on undefined
In Opera version 8 on 2005-04-19
In Opera Android version 10.1 on 2010-11-09
In Safari version 1.2 on 2004-02-02
In Safari on iOS version 1 on 2007-06-29
In Samsung Internet version 1.0 on 2013-04-27
In WebView Android version 4.4 on 2013-12-09
In WebView on iOS version 1 on 2007-06-29