Saving files in a Chrome App

Question

Summary

Normally I could download a bunch of files, but Chrome Apps won't show the download shelf when a download occurs. What would be the best way of getting around this limitation of Chrome Apps?

Ideas

• I could go about this by creating a zip file, but this would require the user to perform an extra step of unzipping the file.
• I'm able to silently download the files, and so I could display a prompt to the user when the file is downloaded, but this would require the user to manually search for the file in their downloads folder.

What I've Learned

• Everywhere on the internet tells me to use Chrome's download API, but this only works for Chrome extensions and not Chrome apps.
• I can't bring up a save as window because 50 save as windows for 50 files is unacceptable
• I can, however, bring up a prompt using chrome.fileSystem.chooseEntry({'type': "openDirectory"} to ask the user to choose a directory, but I can't find a way of saving to that directory.
• My question is basically the same as How can a Chrome extension save many files to a user-specified directory? but for a Chrome app instead of an extension.

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Project and Example Code

The app I'm building will be the same as this webpage I've built, but with a few modifications to make it work as a web-app.

This is how my website solves the problem

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let a = document.createElement("a");
a.href = example_pic;

document.body.appendChild(a)
a.click();

window.URL.revokeObjectURL(a.href);
a.remove()

Answer 1

I can, however, bring up a prompt using chrome.fileSystem.chooseEntry({'type': "openDirectory"}) to ask the user to choose a directory, but I can't find a way of saving to that directory.

That's what you need to work on.

Suppose you declare all the sub-permissions for the fileSystem API:

"permissions": [
   {"fileSystem": ["write", "retainEntries", "directory"]}
]

Then you can:

1. Get an entry from the user:

   chrome.fileSystem.chooseEntry({'type': "openDirectory"}, function(dirEntry) {
     // Check for chrome.runtime.lastError, then use dirEntry
   });
   

2. Retain it, so you can reuse it later without asking the user again:

   dirEntryId = chrome.fileSystem.retainEntry(dirEntry);
   
   // Use chrome.storage to save/retrieve it
   
   chrome.fileSystem.restoreEntry(dirEntryId, function(entry) { /* ... */ });
   

3. Using the HTML FileSystem API, create files in the directory:

   dirEntry.getFile(
     "test.txt",
     {create: true}, // add "exclusive: true" to prevent overwrite
     function(fileEntry) { /* write here */ },
     function(e) { console.error(e) }
   );