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How to create a file in memory for user to download, but not through server?
(22 answers)
Closed 2 years ago.
I have data that I want to write to a file, and open a file dialog for the user to choose where to save the file. It would be great if it worked in all browsers, but it has to work in Chrome. I want to do this all client-side.
Basically I want to know what to put in this function:
saveFile: function(data)
{
}
Where the function takes in data, has the user select a location to save the file, and creates a file in that location with that data.
Using HTML is fine too, if that helps.
A very minor improvement of the code by Awesomeness01 (no need for anchor tag) with addition as suggested by trueimage (support for IE):
// Function to download data to a file
function download(data, filename, type) {
var file = new Blob([data], {type: type});
if (window.navigator.msSaveOrOpenBlob) // IE10+
window.navigator.msSaveOrOpenBlob(file, filename);
else { // Others
var a = document.createElement("a"),
url = URL.createObjectURL(file);
a.href = url;
a.download = filename;
document.body.appendChild(a);
a.click();
setTimeout(function() {
document.body.removeChild(a);
window.URL.revokeObjectURL(url);
}, 0);
}
}
Tested to be working properly in Chrome, FireFox and IE10.
In Safari, the data gets opened in a new tab and one would have to manually save this file.
function download(text, name, type) {
var a = document.getElementById("a");
var file = new Blob([text], {type: type});
a.href = URL.createObjectURL(file);
a.download = name;
}
click here to download your file
<button onclick="download('file text', 'myfilename.txt', 'text/plain')">Create file</button>
And you would then download the file by putting the download attribute on the anchor tag.
The reason I like this better than creating a data url is that you don't have to make a big long url, you can just generate a temporary url.
This project on github looks promising:
https://github.com/eligrey/FileSaver.js
FileSaver.js implements the W3C saveAs() FileSaver interface in
browsers that do not natively support it.
Also have a look at the demo here:
http://eligrey.com/demos/FileSaver.js/
Choosing the location to save the file before creating it is not possible. But it is possible, at least in Chrome, to generate files using just JavaScript. Here is an old example of mine of creating a CSV file. The user will be prompted to download it. This, unfortunately, does not work well in other browsers, especially IE.
<!DOCTYPE html>
<html>
<head>
<title>JS CSV</title>
</head>
<body>
<button id="b">export to CSV</button>
<script type="text/javascript">
function exportToCsv() {
var myCsv = "Col1,Col2,Col3\nval1,val2,val3";
window.open('data:text/csv;charset=utf-8,' + escape(myCsv));
}
var button = document.getElementById('b');
button.addEventListener('click', exportToCsv);
</script>
</body>
</html>
For latest browser, like Chrome, you can use the File API as in this tutorial:
window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem;
window.requestFileSystem(window.PERSISTENT, 5*1024*1024 /*5MB*/, saveFile, errorHandler);
function SaveBlobAs(blob, file_name) {
if (typeof navigator.msSaveBlob == "function")
return navigator.msSaveBlob(blob, file_name);
var saver = document.createElementNS("http://www.w3.org/1999/xhtml", "a");
var blobURL = saver.href = URL.createObjectURL(blob),
body = document.body;
saver.download = file_name;
body.appendChild(saver);
saver.dispatchEvent(new MouseEvent("click"));
body.removeChild(saver);
URL.revokeObjectURL(blobURL);
}
Tried this in the console, and it works.
var aFileParts = ['<a id="a"><b id="b">hey!</b></a>'];
var oMyBlob = new Blob(aFileParts, {type : 'text/html'}); // the blob
window.open(URL.createObjectURL(oMyBlob));
You cannot do this purely in Javascript. Javascript running on browsers does not have enough permission yet (there have been proposals) due to security reasons.
Instead, I would recommend using Downloadify:
A tiny javascript + Flash library that enables the creation and download of text files without server interaction.
You can see a simple demo here where you supply the content and can test out saving/cancelling/error handling functionality.
For Chrome and Firefox, I have been using a purely JavaScript method.
(My application cannot make use of a package such as Blob.js because it is served from a special engine: a DSP with a WWWeb server crammed in and little room for anything at all.)
function FileSave(sourceText, fileIdentity) {
var workElement = document.createElement("a");
if ('download' in workElement) {
workElement.href = "data:" + 'text/plain' + "charset=utf-8," + escape(sourceText);
workElement.setAttribute("download", fileIdentity);
document.body.appendChild(workElement);
var eventMouse = document.createEvent("MouseEvents");
eventMouse.initMouseEvent("click", true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
workElement.dispatchEvent(eventMouse);
document.body.removeChild(workElement);
} else throw 'File saving not supported for this browser';
}
Notes, caveats, and weasel-words:
I have had success with this code in both Chrome and Firefox clients running in Linux (Maipo) and Windows (7 and 10) environments.
However, if sourceText is larger than a MB, Chrome sometimes (only sometimes) gets stuck in its own download without any failure indication; Firefox, so far, has not exhibited this behavior. The cause might be some blob limitation in Chrome. Frankly, I just don't know; if anybody has any ideas how to correct (or at least detect), please post. If the download anomaly occurs, when the Chrome browser is closed, it generates a diagnostic such as
This code is not compatible with Edge or Internet Explorer; I have not tried Opera or Safari.
StreamSaver is an alternative to save very large files without having to keep all data in the memory.In fact it emulates everything the server dose when saving a file but all client side with service worker.
You can either get the writer and manually write Uint8Array's to it or pipe a binary readableStream to the writable stream
There is a few example showcasing:
How to save multiple files as a zip
piping a readableStream from eg Response or blob.stream() to StreamSaver
manually writing to the writable stream as you type something
or recoding a video/audio
Here is an example in it's simplest form:
const fileStream = streamSaver.createWriteStream('filename.txt')
new Response('StreamSaver is awesome').body
.pipeTo(fileStream)
.then(success, error)
If you want to save a blob you would just convert that to a readableStream
new Response(blob).body.pipeTo(...) // response hack
blob.stream().pipeTo(...) // feature reference
Javascript has a FileSystem API. If you can deal with having the feature only work in Chrome, a good starting point would be: http://www.html5rocks.com/en/tutorials/file/filesystem/.
I'm trying to find a cross browser way to store data locally in HTML5. I have generated a chunk of data in a Blob (see MDN). Now I want to move this Blob to the actual filesystem and save it locally. I've found the following ways to achieve this;
Use the <a download> attribute. This works only in Chrome currently.
Microsoft introduces a saveAs function in IE 10 which will achieve this.
Open the Blob URL in the browser and save it that way.
None of these seems to work in Safari though. While (1) works in Chrome, (2) in IE and (3) in Firefox no one works in Safari 6. The download attribute is not yet implemented and when trying to open a blob using the URL Safari complains that URLs starting with blob: are not valid URLs.
There is a good script that encapsulates (1) and (3) called FileSaver.js but that does not work using the latest Safari version.
Is there a way to save Blobs locally in a cross browser fashion?
FileSaver.js has beed updated recently and it works on IE10, Safari5+ etc.
See: https://github.com/eligrey/FileSaver.js/#supported-browsers
The file name sucks, but this works for me in Safari 8:
window.open('data:attachment/csv;charset=utf-8,' + encodeURI(csvString));
UPDATE: No longer working in Safari 9.x
The only solution that I have come up with is making a data: url instead. For me this looks like:
window.open("data:image/svg+xml," + encodeURIComponent(currentSVGString));
Here data is the array buffer data coming from response while making http rest call in js. This works in safari, however there might me some issue in filename as it comes to be untitled.
var binary = '';
var bytes = new Uint8Array(data);
var len = bytes.byteLength;
for (var i = 0; i < len; i++) {
binary += String.fromCharCode(bytes[i]);
}
var base64 = 'data:' + contentType + ';base64,' + window.btoa(binary);
var uri = encodeURI(base64);
var anchor = document.createElement('a');
document.body.appendChild(anchor);
anchor.href = uri;
anchor.download = fileName;
anchor.click();
document.body.removeChild(anchor);
Have you read this article? http://updates.html5rocks.com/2012/06/Don-t-Build-Blobs-Construct-Them
Relating to http://caniuse.com/#search=blob, blobs are possible to use in safari.
You should consturct a servlet which delivers the blob via standard http:// url, so you can avoid using blob: url. Just make a request to that url and build your blob.
Afterwards you can save it in your filesystem or local storage.
The download attribute is supported since ~safari 10.1, so currently this is the way to go.
This is the only thing that worked for me on safari.
var newWindow = window.open();
const blobPDF = await renderMapPDF(); // Your async stuff goes here
if (!newWindow) throw new Error('Window could not be opened.');
newWindow.location = URL.createObjectURL(blobPDF);
I am working on uploading image file to TWITPIC using XMLHttp Request on a Chrome Extension . I need to send the image as payload. Is there a way to do this ? I found this link Convert an image into binary data in javascript
But that works on image tags. i need a way to specify image file path and upload image to TWITPIC.
I came to know about FileReader API with HTML 5. Is there any way to work using that??. It should work on a local file.
Does Chrome Extension support FileReader API without running a localhost server ??
I found the answer myself. Chrome Extensions does support FileReader API of HTML 5. So just the code below works simple.
var reader = new FileReader();
reader.readAsDataURL(f);
You can use this to get the binary data of an image using XMLHTTPRequests, I used it recently for a similar purpose:
var dataToBinary = function(data){
var data_string = "";
for(var i=0; i<data.length; i++){
data_string += String.fromCharCode(data[i].charCodeAt(0) & 0xff);
}
return data_string;
};
$.ajax("http://some.site.com/myImage.jpg", {
success: function(data){
binary = dataToBinary(data);
//or: 'binary = data', dataToBinary might not be needed
},
mimeType: "text/plain; charset=x-user-defined"
});
And the binary data is stored in the binary variable.
I have an image encoded in base64 in a javascript variable : data:image/png;base64, base64 data
[EDIT]
I need to save that file to disk without asking to the visitor to do a right click
[/EDIT]
Is it possible ? How ?
Thanks in advance
Best regards
I know this question is 2 years old, but hopefully people will see this update.
You can prompt the user to save an image in a base64 string (and also set the filename), without asking the user to do a right click
var download = document.createElement('a');
download.href = dataURI;
download.download = filename;
download.click();
Example:
var download = document.createElement('a');
download.href = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';
download.download = 'reddot.png';
download.click();
In order to trigger a click event using Firefox, you need to do what it is explained in this SO answer. Basically:
function fireEvent(obj,evt){
var fireOnThis = obj;
if(document.createEvent ) {
var evObj = document.createEvent('MouseEvents');
evObj.initEvent( evt, true, false );
fireOnThis.dispatchEvent( evObj );
} else if( document.createEventObject ) {
var evObj = document.createEventObject();
fireOnThis.fireEvent( 'on' + evt, evObj );
}
}
fireEvent(download, 'click')
As of 20/03/2013, the only browser that fully supports the download attribute is Chrome. Check the compatibility table here
... without asking to the visitor anyhing ... Is it possible?
No, that would have been a security hole. If it was possible, one would be able to write malware to the enduser's disk unaskingly. Your best bet may be a (signed) Java Applet. True, it costs a bit of $$$ to get it signed (so that it doesn't pop security warnings), but it is able to write data to enduser's disk without its permission.
I am surprised nobody here mentioned using HTML5 blobs together with a couple of nice libraries.
You first need https://github.com/eligrey/FileSaver.js/ and https://github.com/blueimp/JavaScript-Canvas-to-Blob.
Then you can load the image into a canvas
base_image = new Image();
base_image.src ='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==';
the canvas into a blob
var canvas = document.getElementById('YourCanvas');
context = canvas.getContext('2d');
// Draw image within
context.drawImage(base_image, 0,0);
and finally save it
x_canvas.toBlob(function(blob) {
saveAs(blob, "screenshot.png");
}, "image/png");
FF is not fully supported but at least you get a separate page with the image.
Check this out: http://jsfiddle.net/khhmm/9/
EDIT: this is not compatible with Safari / Mac.
As other answers already stated, you cannot do it only with javascript. If you want, you can send the data (using normal HTTP POST) to a PHP script, call header('Content-type: image/png') and output the decoded image data to the page using echo base64_decode($base64data).
This will work just as if user clicked on an image and open it or prompt him to save the file to disk (the normal browser's save file dialog).
It's not possible.
If it was, browsers would be massively insecure, being able to write random data to your hard disk without user interaction.
with javascript, you can't. the only real possibility i can think of will be a java-applet, but maybe (i don't know how long that image should be saved) you could simply add an img-tag with you png and force caching (but if the user deletes his cache, the image will be gone).
I think it's possible with JavaScript if you use ActiveX.
Another possibility is to make the server spit out that file with a different mime type so the browser asks the user to save it.
I think you can do it something(maybe not only with javascript...xul programming needed). There are Firefox addons that save images to a folder(check Firefox addons site)
You can make this file as blob on the server and use setTimeout function in order to fire the download.
The accepted solution seems to have a limitation for large data. If you're running into this (instead of the downloaded file's name, I see "download" and "Failed - Network error" in Chrome), here's what I did in order to download a 2mb file:
const blob = await (await fetch(document.getElementById('canvasID').toDataURL())).blob();
const file = new File([blob], {type:"image/png", lastModified: new Date()});
var a = document.createElement('a');
a.href = window.URL.createObjectURL(file);
a.download = 'image.png';
a.click();
I have upload file functionality on one of the page. I check for the extension of the file using JavaScript. Now i want to restrict the user from uploading file greater than 1 MB. Is there any way i can check the file upload size using JavaScript.
My code currently look like this:
<script language="JavaScript">
function validate() {
var filename = document.getElementById("txtChooseFile").value;
var ext = getExt(filename);
if(ext == "txt" || ext == "csv")
return true;
alert("Please upload Text files only.");
return false;
}
function getExt(filename) {
var dot_pos = filename.lastIndexOf(".");
if(dot_pos == -1)
return "";
return filename.substr(dot_pos+1).toLowerCase();
}
</script>
See http://www.w3.org/TR/FileAPI/. It is supported by Firefox 3.6; I don't know about any other browsers.
Within the onchange event of a <input id="fileInput" type="file" /> simply:
var fi = document.getElementById('fileInput');
alert(fi.files[0].size); // maybe fileSize, I forget
You can also return the contents of the file as a string, and so forth. But again, this may only work with Firefox 3.6.
Now it is possible to get file size using pure JavaScript. Nearly all browser support FileReader, which you can use to read file size as well as you can show image without uploading file to server. link
Code:
var oFile = document.getElementById("file-input").files[0]; // input box with type file;
var img = document.getElementById("imgtag");
var reader = new FileReader();
reader.onload = function (e) {
console.log(e.total); // file size
img.src = e.target.result; // putting file in dom without server upload.
};
reader.readAsDataURL(oFile );
You can get file size directly from file object using following code.
var fileSize = oFile.size;
Other that aquiring the filename there is no way for you to find out any other details about the file in javascript including its size.
Instead you should configure server-side script to block an oversized upload.
Most of these answers are way out-of-date. It is currently possible to determine file size client-side in any browser that supports the File API. This includes, pretty much, all browsers other than IE9 and older.
It might be possible using a lot of browser-specific code. Take a look at the source of TiddlyWiki, which manages to save itself on the user's hard drive by hooking into Windows Scripting Host (IE), XPCOM (Mozilla), etc.
I don't think there is any way of doing that with plain JS from a web page.
With a browser extension maybe, but from a page javascript cannot access the filesystem for security reasons.
Flash and Java should have similar restrictions, but maybe they are a bit less strict.
not possible. would be a major security concern to allow client side scripts to run that can read file info from and end users hard drive.
See here:
http://www.kavoir.com/2009/01/check-for-file-size-with-javascript-before-uploading.html
As to all the people saying this has to be done server side, they are absolutely spot on it does.
In my case though the maximum size I will except is 128Mb, if a user tries to upload something that is 130Mb they should not have to wait the 5 minute upload time to find out it is too big so I need to do an additional check before they submit the page for usability sake.
I had the same issue, Here's a simple JavaScript snippet worked for me. Adding for future googlers.
HTML
<input type="file" name="photo" id="photo" accept="image/*">
JS
const file = document.getElementById('photo');
// Show KB (add one more /1024 for MB)
const filesize = file.files[0].size / 1024;
if (filesize > 500) { // Alert greater than 500kb
console.log(filesize);
alert('Please upload image less than 500 KB');
return;
}