CODEWITHSUNDEEP
javascripthtmldownload
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Reputation: 34498

Using HTML5/JavaScript to generate and save a file

I've been fiddling with WebGL lately, and have gotten a Collada reader working. Problem is it's pretty slow (Collada is a very verbose format), so I'm going to start converting files to a easier to use format (probably JSON). I already have the code to parse the file in JavaScript, so I may as well use it as my exporter too! The problem is saving.

Now, I know that I can parse the file, send the result to the server, and have the browser request the file back from the server as a download. But in reality the server has nothing to do with this particular process, so why get it involved? I already have the contents of the desired file in memory. Is there any way that I could present the user with a download using pure JavaScript? (I doubt it, but might as well ask...)

And to be clear: I am not trying to access the filesystem without the users knowledge! The user will provide a file (probably via drag and drop), the script will transform the file in memory, and the user will be prompted to download the result. All of which should be "safe" activities as far as the browser is concerned.

[EDIT]: I didn't mention it upfront, so the posters who answered "Flash" are valid enough, but part of what I'm doing is an attempt to highlight what can be done with pure HTML5... so Flash is right out in my case. (Though it's a perfectly valid answer for anyone doing a "real" web app.) That being the case it looks like I'm out of luck unless I want to involve the server. Thanks anyway!

Upvotes: 371

Views: 497128

Answers (18)

Razakhel
Razakhel

Reputation: 762

I've used FileSaver (https://github.com/eligrey/FileSaver.js) and it works just fine.
For example, I did this function to export logs displayed on a page.
You have to pass an array for the instantiation of the Blob, so I just maybe didn't write this the right way, but it works for me.
Just in case, be careful with the replace: this is the syntax to make this global, otherwise it will only replace the first one it meets.

exportLogs : function(){
    var array = new Array();
    
    var str = $('#logs').html();
    array[0] = str.replace(/<br>/g, '\n\t');
    
    var blob = new Blob(array, {type: "text/plain;charset=utf-8"});
    saveAs(blob, "example.log");
}

Upvotes: 15

bcmpinc
bcmpinc

Reputation: 3370

Updated Answer

As all modern browsers have support for this now. Saving a large file can be performed as shown below. Using application/octet-stream as mime type forces a download.

The code uses window.open to trigger the download, which is blocked inside snippets. This should be used inside a click event handler. Otherwise window.open is hindered by the browser's popup blocker. I'm not sure about the revokeObjectURL line at the end, but it seems to work and otherwise can be left out.

function generate_and_download() {
  const data = [];
  data.push("This is a test\n");
  data.push("Of creating a file\n");
  data.push("In a browser\n");
  const file = new File(data, "file.txt", {type: 'application/octet-stream'});
  var url = URL.createObjectURL(file);
  window.open(url);
  URL.revokeObjectURL(url); // This seems to work here.
}

Old Answer

Saving large files

Long data URIs can give performance problems in browsers. Another option to save client-side generated files, is to put their contents in a Blob (or File) object and create a download link using URL.createObjectURL(blob). This returns an URL that can be used to retrieve the contents of the blob. The blob is stored inside the browser until either URL.revokeObjectURL() is called on the URL or the document that created it is closed. Most web browsers have support for object URLs, Opera Mini is the only one that does not support them.

Forcing a download

If the data is text or an image, the browser can open the file, instead of saving it to disk. To cause the file to be downloaded upon clicking the link, you can use the the download attribute. However, not all web browsers have support for the download attribute. Another option is to use application/octet-stream as the file's mime-type, but this causes the file to be presented as a binary blob which is especially user-unfriendly if you don't or can't specify a filename. See also 'https://stackoverflow.com/q/3802510/558366'.

Specifying a filename

If the blob is created with the File constructor, you can also set a filename, but only a few web browsers (including Chrome & Firefox) have support for the File constructor. The filename can also be specified as the argument to the download attribute, but this is subject to a ton of security considerations. Internet Explorer 10 and 11 provides its own method, msSaveBlob, to specify a filename.

Example code

var file;
var data = [];
data.push("This is a test\n");
data.push("Of creating a file\n");
data.push("In a browser\n");
var properties = {type: 'text/plain'}; // Specify the file's mime-type.
try {
  // Specify the filename using the File constructor, but ...
  file = new File(data, "file.txt", properties);
} catch (e) {
  // ... fall back to the Blob constructor if that isn't supported.
  file = new Blob(data, properties);
}
var url = URL.createObjectURL(file);
document.getElementById('link').href = url;
<a id="link" target="_blank" download="file.txt">Download</a>

Upvotes: 65

User
User

Reputation: 357

You can use this to save text and other data:

function downloadFile(name, data) {
    let a = document.createElement("a");
    if (typeof a.download !== "undefined") a.download = name;
    a.href = URL.createObjectURL(new Blob([data], {
        type: "application/octet-stream"
    }));
    a.dispatchEvent(new MouseEvent("click"));
}

This function will create an Anchor element, set the name via .download (if supported), assign a url (.href) created from an object (URL.createObjectURL), in this case a Blob object, and dispatch a click event. In short: it's as if you're clicking a download link.

Example code

downloadFile("textfile.txt", "A simple text file");
downloadFile(
    "circle.svg",
    `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 100 100">
        <circle cx="50" cy="50" r="42" />
    </svg>`
);
downloadFile(
    "utf8string.txt",
    new Uint8Array([85, 84, 70, 45, 56, 32, 115, 116, 114, 105, 110, 103]) // "UTF-8 string"
);

This function also accepts File, Blob and MediaSource:

function downloadFile(name, data) {
    if (!(data instanceof File || data instanceof Blob || data instanceof MediaSource)) {
        return downloadFile(name, new Blob([data], {
            type: "application/octet-stream"
        }));
    }

    let a = document.createElement("a");
    if (typeof a.download !== "undefined") a.download = name;
    a.href = URL.createObjectURL(data);
    a.dispatchEvent(new MouseEvent("click"));
}

Or you could use two functions:

function downloadFile(name, data) {
    return downloadObject(new Blob([data], {
        type: "application/octet-stream"
    }));
}

function downloadObject(name, object) {
    let a = document.createElement("a");
    if (typeof a.download !== "undefined") a.download = name;
    a.href = URL.createObjectURL(object);
    a.dispatchEvent(new MouseEvent("click"));
}

Upvotes: 4

Peeter Vois
Peeter Vois

Reputation: 86

When testing the "ahref" method, I found that the web developer tools of Firefox and Chrome gets confused. I needed to restart the debugging after the a.click() was issued. Same happened with the FileSaver (it uses the same ahref method to actually make the saving). To work around it, I created new temporary window, added the element a into that and clicked it there.

    function download_json(dt) {
        var csv = ' var data = ';
        csv += JSON.stringify(dt, null, 3);

        var uricontent = 'data:application/octet-stream,' + encodeURI(csv);

        var newwin = window.open( "", "_blank" );
        var elem = newwin.document.createElement('a');
        elem.download = "database.js";
        elem.href = uricontent;
        elem.click();
        setTimeout(function(){ newwin.close(); }, 3000);
        
    }

Upvotes: 2

Kamil Kiełczewski
Kamil Kiełczewski

Reputation: 92347

try

let a = document.createElement('a');
a.href = "data:application/octet-stream,"+encodeURIComponent('"My DATA"');
a.download = 'myFile.json';
a.click(); // we not add 'a' to DOM so no need to remove

If you want to download binary data look here

Update

2020.06.14 I upgrade Chrome to 83.0 and above SO snippet stop works (due to sandbox security restrictions) - but JSFiddle version works - here

Upvotes: 11

tgraupmann
tgraupmann

Reputation: 71

This thread was invaluable to figure out how to generate a binary file and prompt to download the named file, all in client code without a server.

First step for me was generating the binary blob from data that I was saving. There's plenty of samples for doing this for a single binary type, in my case I have a binary format with multiple types which you can pass as an array to create the blob.

saveAnimation: function() {

    var device = this.Device;
    var maxRow = ChromaAnimation.getMaxRow(device);
    var maxColumn = ChromaAnimation.getMaxColumn(device);
    var frames = this.Frames;
    var frameCount = frames.length;

    var writeArrays = [];


    var writeArray = new Uint32Array(1);
    var version = 1;
    writeArray[0] = version;
    writeArrays.push(writeArray.buffer);
    //console.log('version:', version);


    var writeArray = new Uint8Array(1);
    var deviceType = this.DeviceType;
    writeArray[0] = deviceType;
    writeArrays.push(writeArray.buffer);
    //console.log('deviceType:', deviceType);


    var writeArray = new Uint8Array(1);
    writeArray[0] = device;
    writeArrays.push(writeArray.buffer);
    //console.log('device:', device);


    var writeArray = new Uint32Array(1);
    writeArray[0] = frameCount;
    writeArrays.push(writeArray.buffer);
    //console.log('frameCount:', frameCount);

    for (var index = 0; index < frameCount; ++index) {

      var frame = frames[index];

      var writeArray = new Float32Array(1);
      var duration = frame.Duration;
      if (duration < 0.033) {
        duration = 0.033;
      }
      writeArray[0] = duration;
      writeArrays.push(writeArray.buffer);

      //console.log('Frame', index, 'duration', duration);

      var writeArray = new Uint32Array(maxRow * maxColumn);
      for (var i = 0; i < maxRow; ++i) {
        for (var j = 0; j < maxColumn; ++j) {
          var color = frame.Colors[i][j];
          writeArray[i * maxColumn + j] = color;
        }
      }
      writeArrays.push(writeArray.buffer);
    }

    var blob = new Blob(writeArrays, {type: 'application/octet-stream'});

    return blob;
}

The next step is to get the browser to prompt the user to download this blob with a predefined name.

All I needed was a named link I added in the HTML5 that I could reuse to rename the initial filename. I kept it hidden since the link doesn't need display.

<a id="lnkDownload" style="display: none" download="client.chroma" href="" target="_blank"></a>

The last step is to prompt the user to download the file.

var data = animation.saveAnimation();
var uriContent = URL.createObjectURL(data);
var lnkDownload = document.getElementById('lnkDownload');
lnkDownload.download = 'theDefaultFileName.extension';
lnkDownload.href = uriContent;
lnkDownload.click();

Upvotes: 2

T.Todua
T.Todua

Reputation: 56341

Simple Solution!

<a download="My-FileName.txt" href="data:application/octet-stream,HELLO-WORLDDDDDDDD">Click here</a>

Works in all Modern browsers.

Upvotes: 20

Ilyas karim
Ilyas karim

Reputation: 4812

Here is a tutorial to export files as ZIP:

Before getting started, there is a library to save files, the name of library is fileSaver.js, You can find this library here. Let's get started, Now, include the required libraries:

<script src="https://cdnjs.cloudflare.com/ajax/libs/jszip/3.1.4/jszip.min.js"  type="text/javascript"></script>
<script type="text/javascript" src="https://fastcdn.org/FileSaver.js/1.1.20151003/FileSaver.js" ></script>

Now copy this code and this code will download a zip file with a file hello.txt having content Hello World. If everything thing works fine, this will download a file.

<script type="text/javascript">
    var zip = new JSZip();
    zip.file("Hello.txt", "Hello World\n");
    zip.generateAsync({type:"blob"})
    .then(function(content) {
        // see FileSaver.js
        saveAs(content, "file.zip");
    });
</script>

This will download a file called file.zip. You can read more here: http://www.wapgee.com/story/248/guide-to-create-zip-files-using-javascript-by-using-jszip-library

Upvotes: 1

Kevin
Kevin

Reputation: 2697

As previously mentioned the File API, along with the FileWriter and FileSystem APIs can be used to store files on a client's machine from the context of a browser tab/window.

However, there are several things pertaining to latter two APIs which you should be aware of:

  • Implementations of the APIs currently exist only in Chromium-based browsers (Chrome & Opera)
  • Both of the APIs were taken off of the W3C standards track on April 24, 2014, and as of now are proprietary
  • Removal of the (now proprietary) APIs from implementing browsers in the future is a possibility
  • A sandbox (a location on disk outside of which files can produce no effect) is used to store the files created with the APIs
  • A virtual file system (a directory structure which does not necessarily exist on disk in the same form that it does when accessed from within the browser) is used represent the files created with the APIs

Here are simple examples of how the APIs are used, directly and indirectly, in tandem to do this:

BakedGoods*

bakedGoods.get({
        data: ["testFile"],
        storageTypes: ["fileSystem"],
        options: {fileSystem:{storageType: Window.PERSISTENT}},
        complete: function(resultDataObj, byStorageTypeErrorObj){}
});

Using the raw File, FileWriter, and FileSystem APIs

function onQuotaRequestSuccess(grantedQuota)
{

    function saveFile(directoryEntry)
    {

        function createFileWriter(fileEntry)
        {

            function write(fileWriter)
            {
                var dataBlob = new Blob(["Hello world!"], {type: "text/plain"});
                fileWriter.write(dataBlob);              
            }

            fileEntry.createWriter(write);
        }

        directoryEntry.getFile(
            "testFile", 
            {create: true, exclusive: true},
            createFileWriter
        );
    }

    requestFileSystem(Window.PERSISTENT, grantedQuota, saveFile);
}

var desiredQuota = 1024 * 1024 * 1024;
var quotaManagementObj = navigator.webkitPersistentStorage;
quotaManagementObj.requestQuota(desiredQuota, onQuotaRequestSuccess);

Though the FileSystem and FileWriter APIs are no longer on the standards track, their use can be justified in some cases, in my opinion, because:

  • Renewed interest from the un-implementing browser vendors may place them right back on it
  • Market penetration of implementing (Chromium-based) browsers is high
  • Google (the main contributer to Chromium) has not given and end-of-life date to the APIs

Whether "some cases" encompasses your own, however, is for you to decide.

*BakedGoods is maintained by none other than this guy right here :)

Upvotes: 4

N&#248;k
N&#248;k

Reputation: 2764

OK, creating a data:URI definitely does the trick for me, thanks to Matthew and Dennkster pointing that option out! Here is basically how I do it:

1) get all the content into a string called "content" (e.g. by creating it there initially or by reading innerHTML of the tag of an already built page).

2) Build the data URI:

uriContent = "data:application/octet-stream," + encodeURIComponent(content);

There will be length limitations depending on browser type etc., but e.g. Firefox 3.6.12 works until at least 256k. Encoding in Base64 instead using encodeURIComponent might make things more efficient, but for me that was ok.

3) open a new window and "redirect" it to this URI prompts for a download location of my JavaScript generated page:

newWindow = window.open(uriContent, 'neuesDokument');

That's it.

Upvotes: 274

Matěj Pokorn&#253;
Matěj Pokorn&#253;

Reputation: 17835

Simple solution for HTML5 ready browsers...

function download(filename, text) {
    var pom = document.createElement('a');
    pom.setAttribute('href', 'data:text/plain;charset=utf-8,' + encodeURIComponent(text));
    pom.setAttribute('download', filename);

    if (document.createEvent) {
        var event = document.createEvent('MouseEvents');
        event.initEvent('click', true, true);
        pom.dispatchEvent(event);
    }
    else {
        pom.click();
    }
}

Usage

download('test.txt', 'Hello world!');

Upvotes: 335

maikel
maikel

Reputation: 1779

I found two simple approaches that work for me. First, using an already clicked a element and injecting the download data. And second, generating an a element with the download data, executing a.click() and removing it again. But the second approach works only if invoked by a user click action as well. (Some) Browser block click() from other contexts like on loading or triggered after a timeout (setTimeout).

<!DOCTYPE HTML>
<html>
  <head>
    <meta charset="UTF-8">
    <script type="text/javascript">
      function linkDownload(a, filename, content) {
        contentType =  'data:application/octet-stream,';
        uriContent = contentType + encodeURIComponent(content);
        a.setAttribute('href', uriContent);
        a.setAttribute('download', filename);
      }
      function download(filename, content) {
        var a = document.createElement('a');
        linkDownload(a, filename, content);
        document.body.appendChild(a);
        a.click();
        document.body.removeChild(a);
      }
    </script>
   </head>
  <body>
    <a href="#" onclick="linkDownload(this, 'test.txt', 'Hello World!');">download</a>
    <button onclick="download('test.txt', 'Hello World!');">download</button>
  </body>
</html>

Upvotes: 9

panzi
panzi

Reputation: 7702

HTML5 defined a window.saveAs(blob, filename) method. It isn't supported by any browser right now. But there is a compatibility library called FileSaver.js that adds this function to most modern browsers (including Internet Explorer 10+). Internet Explorer 10 supports a navigator.msSaveBlob(blob, filename) method (MSDN), which is used in FileSaver.js for Internet Explorer support.

I wrote a blog posting with more details about this problem.

Upvotes: 84

Yassir Ennazk
Yassir Ennazk

Reputation: 7169

function download(content, filename, contentType)
{
    if(!contentType) contentType = 'application/octet-stream';
        var a = document.createElement('a');
        var blob = new Blob([content], {'type':contentType});
        a.href = window.URL.createObjectURL(blob);
        a.download = filename;
        a.click();
}

Upvotes: 42

Pekka
Pekka

Reputation: 449385

Take a look at Doug Neiner's Downloadify which is a Flash based JavaScript interface to do this.

Downloadify is a tiny JavaScript + Flash library that enables the generation and saving of files on the fly, in the browser, without server interaction.

Upvotes: 24

Dennkster
Dennkster

Reputation: 2271

Here is a link to the data URI method Mathew suggested, it worked on safari, but not well because I couldn't set the filetype, it gets saved as "unknown" and then i have to go there again later and change it in order to view the file...

http://www.nihilogic.dk/labs/canvas2image/

Upvotes: 6

Jeanine
Jeanine

Reputation: 73

You can use localStorage. This is the Html5 equivalent of cookies. It appears to work on Chrome and Firefox BUT on Firefox, I needed to upload it to a server. That is, testing directly on my home computer didn't work.

I'm working up HTML5 examples. Go to http://faculty.purchase.edu/jeanine.meyer/html5/html5explain.html and scroll to the maze one. The information to re-build the maze is stored using localStorage.

I came to this article looking for HTML5 JavaScript for loading and working with xml files. Is it the same as older html and JavaScript????

Upvotes: 4

Matthew Flaschen
Matthew Flaschen

Reputation: 284786

You can generate a data URI. However, there are browser-specific limitations.

Upvotes: 11

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