Accessing the user's preferences in terms of tracking can be slightly complicated. This module simplifies that.
npm install --save donottrack
Browser:
import doNotTrack from 'donottrack';
// Returns true if the user agrees to being tracked, false otherwise.
const mayTrack = doNotTrack(/* default, if preferences are not set. */ true);
Node:
import doNotTrack from 'donottrack';
const mayTrack = doNotTrack(req.header('DNT'), true);