How to force Chrome to NOT open SaveAs Dialog when downloading a URL?

Question

Chrome Build: the newest, 33+

A Chrome Extension extracts certain urls from currently viewed site and then downloads a subset of them (quite often hundreds of files).

Answer 1

Edit : I've added complete sample code for multiple file downloads which doesn't show SaveAs Dialog.

You can achieve this by using chrome.downloads API.

manifest.json

{
  "description": "Multiple file downloads without showing SaveAs Dialog",
  "background": {
     "scripts": [ "background.js" ],
     "persistent" : true
  },
  "content_scripts": [{
     "js": [ "content_script.js"],
     "matches": [ "<all_urls>" ],
     "run_at": "document_start"
  }],
  "manifest_version": 2,
  "name": "MultipleFileDownloads",
  "permissions": [ "downloads" ],
  "short_name": "MFD",
  "version": "0.0.0.1"
}

content_script.js

var DOWNLOAD_LIMIT = 100;

function downloadURL(url, filename, callback){
    chrome.runtime.sendMessage({
        download_url : url,
        filename : filename
    },function(){
        if(typeof callback == 'function'){
            callback();
        }
    })
}

function simulateFileDownload(i){
    if(i > DOWNLOAD_LIMIT){
        document.getElementById('download_btn').disabled = false;
        return false;
    }
    var blob = new Blob(['This is sample file '+i], {type:'text/plain'});
    var url = URL.createObjectURL(blob);
    downloadURL(url,'Sample-'+i+'.txt',function(){
        URL.revokeObjectURL(url);
        i++;
        simulateFileDownload(i);
    })
}

window.onload = function(){
    var btn = document.createElement('button');
    btn.id = 'download_btn';
    btn.style.cssText = 'position:fixed;top:10px;left:10px;width:140px;height:30px;z-index:1000000;';
    btn.textContent = 'Download Files';
    document.body.appendChild(btn);
    btn.addEventListener('click',function(){
        this.disabled = true;
        simulateFileDownload(0);
    })
}

background.js

chrome.runtime.onMessage.addListener(function(message, sender, sendResponse){
    if(message.download_url){
        chrome.downloads.download({
            url : message.download_url,
            filename : message.filename,
            saveAs : false
        }
    }
});

Answer 2

It is impossible when "Ask where to save each file before downloading" Enabled (as of 70.0.3538.77). The corresponding Chromium bug is:

Bug 417112: chrome.downloads.download ignore saveAs

Moreover setting filename in chrome.downloads.downloads() also doesn't work.

Bug 758094: Extension can not rename downloaded file