Is it possible to check the value of Firefox DNT with javascript?

Question

I\'m working on a javascript advertising engine, and I would like for it to respect Firefox DNT header.

Is there any way javascript can check if the user has set DNT to

Answer 1

I think you're looking for navigator.doNotTrack:

console.log(window.navigator.doNotTrack); 
// prints "yes" if DNT is enabled; otherwise this is "unspecified" in Firefox

MDN explains that in Firefox:

When the do-not-track header sends "1", navigator.doNotTrack is "yes". When the header is unset, navigator.doNotTrack is "unspecified". When the header sends "0" (currently unsupported in Firefox), navigator.doNotTrack is "no".

In other browsers:

IE9, Opera 12, and Safari 5.1 are based on an earlier version of this specification where navigator.doNotTrack is the value sent for the do-not-track header.

IE9 uses a vendor prefix, i.e., navigator.msDoNotTrack

So, you might detect DNT in general by doing:

var isDNT = navigator.doNotTrack == "yes" || navigator.doNotTrack == "1" || 
              navigator.msDoNotTrack == "1";