How to minify files using only uglifyjs?

I have tried to minify javascript files using uglifyjs, but it's only outputting the file name in the file output.min.js followed by a semicolon and it's telling me that "File was successfully saved."; Not the minified code of the js file geolocation.service.js. Could anyone please help? The code below is saved in a file that I named uglifyjs. I used $node uglifyjs.js to run the file.

var fs = require('fs');

var uglifyjs = require('uglify-js');

var result = uglifyjs.minify(["geolocation.service.js"]);

console.log(result.code);

fs.writeFile("output.min.js", result.code, function(err){
 if(err){
   console.log(err);
 } else {
  console.log("File was successfully saved.");
 }
   });

via Maz