- // Set the If-Modified-Since header, if ifModified mode.
- if ( s.ifModified )
- xhr.setRequestHeader("If-Modified-Since",
- jQuery.lastModified[s.url] || "Thu, 01 Jan 1970 00:00:00 GMT" );
+ // Set the If-Modified-Since and/or If-None-Match header, if in ifModified mode.
+ if ( s.ifModified ) {
+ if ( jQuery.lastModified[s.url] ) {
+ xhr.setRequestHeader("If-Modified-Since", jQuery.lastModified[s.url]);
+ }
+
+ if ( jQuery.etag[s.url] ) {
+ xhr.setRequestHeader("If-None-Match", jQuery.etag[s.url]);
+ }
+ }