maybe DirectoryReader?

https://developer.mozilla.org/en-US/docs/Web/API/DirectoryReader

    window.requestFileSystem  = window.requestFileSystem || window.webkitRequestFileSystem; 
    window.directoryEntry = window.directoryEntry || window.webkitDirectoryEntry;

    function toArray(list) {
      return Array.prototype.slice.call(list || [], 0);
    }

    function onInitFs(fs) {

      var dirReader = fs.root.createReader();
      var entries = [];

      // Keep calling readEntries() until no more results are returned.
      var readEntries = function() {
         dirReader.readEntries (function(results) {
          if (!results.length) {
              entries.forEach(function(entry, i) {
                var img = entry.isDirectory ? checkFilesAgain(entry) : singlePSD(entry)
                console.log("entry:", entry, "returns:", img)
              });
          } else {
            entries = entries.concat(toArray(results));
            console.log('no results:', entries)
          }
        }, errorHandler);
      };

      readEntries(); 

    }

    window.requestFileSystem(window.TEMPORARY, 1024*1024, onInitFs, errorHandler);