Arnoldiusss Arnoldiusss - 9 months ago 45
Javascript Question

HTML 5 FileSytem, combine FileEntry with MetaData array from callback

In a Chrome extension im using the HTML5 FileSytem API.

Im retrieving a list of records in a folder.

var entries = [];
var metadata = [];

function listFiles(fs) {

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

// Call the reader.readEntries() until no more results are returned.
var readEntries = function () {
dirReader.readEntries(function (results) {
if (!results.length) {
} else {
entries = entries.concat(toArray(results));

readEntries(); // Start reading dirs.


The FileEntry object does not contain metadata, I need the last modified date. I'm able to retrieve a object of metadata

function addMeta(entries) {
for (var i = 0; i < entries.length; i++) {
entries[i].getMetadata(function (metadata) {

Problem is that i get the metadata in a callback.
How can i join the two object making sure the right match is made?
The simplified result im looking for is:

["fileName1", "modifyDate1"],
["fileName2", "modifyDate2"],

Answer Source
  1. To get lastModifiedDate, you don't need to use getMetadata, as per the description of this question, just use entry.file.lastModifiedDate, though maybe file() is another callback.
  2. To "join the two object making sure the right match is made", because of Closures, you could use the following code to get the right results. (Assuming the data structure is [[entry, metadata]] as you mentioned)

    var ans = [];
    function addMeta(entries) {
        for (var i = 0; i < entries.length; i++) {
            (function(entry) {
                entry.getMetadata(function (metadata) {
                    ans.push([entry, metadata]);
  3. If what you want is to wait for all asynchronous callback ends, see this answer for more details, basically you could adjust your code and use Promise, or use other implementations like setInterval or use a variable to calculate how many callbacks remain.