tree.js

var jsroot = require("jsroot");

jsroot.OpenFile("https://root.cern/js/files/hsimple.root", function(f) {
   f.ReadObject("ntuple;1", function(tree) {
      tree.Draw({ expr: "px:py:pz", dump: true, numentries: 100 }, function(res) {
         console.log("NumEntries", res.length);
         var sumx = 0, sumy = 0, sumz = 0;
         res.forEach(function(item) {
            sumx += item.x;
            sumy += item.y;
            sumz += item.z;
         });
         console.log('Mean x', sumx/res.length);
         console.log('Mean y', sumy/res.length);
         console.log('Mean z', sumz/res.length);
      });

   });
});