mine.js

// To start a promise chain from a sync function wrap it with P().
// This is short-hand for creating a deferred and immediately resolving it.
function getFiles(pth) {
  return P(shell.find(pth))
}

// It's ok to put sync function in a promise chain
function filterFolders(data) {
  return data.filter(
    function (file) {
      return !file.match(/\/(node_modules|tests?|automation-tests|example|js\/lib)\//i)
    }
  )
}

function filterJS(data) {
  return data.filter(
    function (file) {
      return file.match(/\.js$/i);
    }
  )
}

// here we take advantage of promises by using the async fs.readFile
function hasCopyright(files) {
  var promises = files.map(
    function (file) {
      var d = P.defer()
      fs.readFile(file, 'utf8', function (err, data) {
        if (err || data.indexOf(COPYRIGHT_HEADER) === -1) {
          return d.reject(err)
        }
        d.resolve(data)
      })
      return d.promise
    }
  )
  return P.allSettled(promises) // allSettled will wait for all promises to finish, then "return" an array of results
    .then(
      function (results) { // allSettled returns both rejected and resolved results, so filter out rejected
        return results.filter(function (r) { return r.state === "fulfilled" }).map(function (r) { return r.value })
      }  
    )
}


function logResults(data) {
   data.forEach(function (file) {
       console.log(file)
   })
}

// chain it all together

getFiles('browserid')
  .then(filterFolders)
  .then(filterJS)
  .then(hasCopyright)
  .done(logResults) // done ensured that any "uncaught" rejects or errors gets rethrown

original.js

#!/usr/bin/env node

var fs = require("fs");

var p = require("p-promise"),
   shell = require("shelljs");

var COPYRIGHT_HEADER = "* This Source Code Form is subject to the terms of the Mozilla Public\n"+
" * License, v. 2.0. If a copy of the MPL was not distributed with this\n"+
" * file, You can obtain one at http://mozilla.org/MPL/2.0/.";

/**
shell.find("browserid").filter(function (file) {
   // We only care about .JS files, presumably.
   return file.match(/\.js$/i);
}).filter(function (file) {
   // Ignore if it's a node module, a test file, or an example file.
   return  !file.match(/\/(node_modules|tests?|automation-tests|example)\//i);
}).forEach(function (file) {
   var data = fs.readFileSync(file, "utf8");
   if (data.indexOf(COPYRIGHT_HEADER) === -1) {
       console.log("No copyright found in: %s", file);
   }
});
*/

getFiles("browserid").then(filterFolders).then(filterJS).then(hasCopyright).then(logResults);



function getFiles(pth) {
   var files = shell.find(pth);
   var deferred = p.defer();
   deferred.resolve(files);
   return deferred.promise;
}

// We only want .js files...
function filterJS(data) {
   var files = data.filter(function (file) {
       return file.match(/\.js$/i);
   });
   var deferred = p.defer();
   deferred.resolve(files);
   return deferred.promise;
}

// But we don't care about the /node_modules/, /test/, /tests/, or /js/lib/ directories.
function filterFolders(data) {
   var files = data.filter(function (file) {
       return !file.match(/\/(node_modules|tests?|automation-tests|example|js\/lib)\//i);
   });
   var deferred = p.defer();
   deferred.resolve(files);
   return deferred.promise;
}

// Sync-load the file and check for the copyright header.
function hasCopyright(data) {
   var files = data.filter(function (file) {
       var contents = fs.readFileSync(file, "utf8");
       return (contents.indexOf(COPYRIGHT_HEADER) === -1);
   });
   var deferred = p.defer();
   deferred.resolve(files);
   return deferred.promise;
}

function logResults(data) {
   data.forEach(function (file) {
       console.log(file);
   });
}