XML : How to append a node in an XML file with node.js fast without string comparison

A solution is proposed here: How to append to certain line of file?

I copy the solution here for reference

  var fs = require('fs');    var xmlFile;  fs.readFile('someFile.xml', function (err, data) {    if (err) throw err;    xmlFile = data;      var newXmlFile = xmlFile.replace('</xml>', '') + 'Content' + '</xml>';      fs.writeFile('someFile.xml', newXmlFile, function (err) {      if (err) throw err;      console.log('Done!');    });   });    

However the solution above requires string matching of the '</xml>' string. If we know that the last line of the file will always be '</xml>' is there any way to speed up the code by eliminating the need for string comparison? Is there an another more efficient way to do this task?