code: function (fileName, fileContents, outFileName, config, pluginCollector) {
              if (!fileContents) {
                  fileContents = file.readFile(fileName);
              }
  
              fileContents = optimize.js(fileName, fileContents, config, pluginCollector);
  
              file.saveUtf8File(outFileName, fileContents);
          }
docs: Optimizes a file that contains JavaScript content. Optionally collects
  plugin resources mentioned in a file, and then passes the content
  through an minifier if one is specified via config.optimize.
  
  @param {String} fileName the name of the file to optimize
  @param {String} fileContents the contents to optimize. If this is
  a null value, then fileName will be used to read the fileContents.
  @param {String} outFileName the name of the file to use for the
  saved optimized content.
  @param {Object} config the build config object.
  @param {Array} [pluginCollector] storage for any plugin resources
  found.