A function to asynchronously confirm the existence of every file in an array.

ifFilesExist.js

  function ifFilesExist (files, cb) {
    var numberOfFiles = files.length
      , returnsChecked = 0
      , existancesConfirmed = 0;

    for (var i = 0; i < numberOfFiles; i++) {
      fs.exists(files[i], next);
    }

    function next (e) {
      returnsChecked++;
      if (e) {
        existancesConfirmed++;
      }

      if (returnsChecked >= numberOfFiles) {
        if (existancesConfirmed >= numberOfFiles) {
          cb(null);
        } else {
          cb(new Error("Not all files exist."));
        }
      }
    }
  }