Develop Reference

Specify the type returned from FileReader readAsDataURL() as PNG and not TIFF?

I'm getting an image that has been pasted into the content editable div and during paste the types in listed in the Clipboard include "image/png" and "image/tiff".
When I get that image using a FileReader and readAsDataURL the base64 image string it returns is a TIFF, "data:image/tiff,".
Is there a way to specify to the FileReader to return a PNG, "data:image/png"?
Related question here.

You don't.
FileReader.readAsDataURL() only converts the binary data held in the passed Blob to a base64 string, it doesn't do any other conversion.
It will only prepend the corresponding MIME header to whatever it thinks this data is (this check is first done against the Blob's type, and then probably against magic-numbers), but you can't force it to convert the data to something else.
const fr = new FileReader();
const fakeGif = new Blob(['foo'], {type:'image/gif'});
fr.onload = onload;
fr.readAsDataURL(fakeGif);
function onload(){
console.log(fr.result); // with image/gif MIME
console.log(atob(fr.result.split(',')[1])) // still just "foo"...
}
Now to your case, since Safari still doesn't support the DataTransferItem interface, you are out of luck.
Even though Grab utility does save a png File in the clipboard, Safari chose to display the tiff raw data.
You can check this assertion in your dev's Network panel, where you will see that the image is fetched as image/tiff.
Browsers that do support DataTransferItem interface can retrieve the png file attached in the clipboard though, so let's hope Safari implement this interface soon enough.
So one way to convert this TIFF image to a png one, is to go through a canvas element:
// an Array to hold pasted Files
var files = [];
// We start by checking if the browser supports the
// DataTransferItem interface. If not, we need to create a
// contenteditable element that catches all pasted data
if (!window.DataTransferItem) {
var pasteCatcher = document.createElement("div");
pasteCatcher.setAttribute("contenteditable", "");
// We can hide the element and append it to the body,
pasteCatcher.style.opacity = 0.5;
document.body.appendChild(pasteCatcher);
// as long as we make sure it is always in focus
pasteCatcher.focus();
document.addEventListener("click", function() {
pasteCatcher.focus();
});
}
// Add the paste event listener
window.addEventListener("paste", pasteHandler);
/* Handle paste events */
function pasteHandler(e) {
// We need to check if event.clipboardData is supported (Chrome)
if (e.clipboardData) {
// Get the items from the clipboard
var items = e.clipboardData.items || e.clipboardData.files;
itemcount = items.length;
if (itemcount) {
// Loop through all items, looking for any kind of image
for (var i = 0; i < items.length; i++) {
getItem(items[i]);
}
} else {
// This is a cheap trick to make sure we read the data
// AFTER it has been inserted.
setTimeout(checkInput, 1);
}
// If we can't handle clipboard data directly (Firefox),
// we need to read what was pasted from the contenteditable element
} else {
console.log("checking input");
// This is a cheap trick to make sure we read the data
// AFTER it has been inserted.
setTimeout(checkInput, 1);
}
}
/* For browsers that support DataTransferItem interface */
function getItem(item)  {
if (item.type.indexOf("image") !== -1) {
// We need to represent the image as a file,
var blob = item instanceof Blob ? item : item.getAsFile();
// save the File for later use if needed
files.push(blob);
// and use a URL or webkitURL (whichever is available to the browser)
// to create a temporary URL to the object
var URLObj = window.URL || window.webkitURL;
var source = URLObj.createObjectURL(blob);
// The URL can then be used as the source of an image
createImage(source);
}
}
/* For older browsers */
/* Parse the input in the paste catcher element */
function checkInput() {
// Store the pasted content in a variable
var child = pasteCatcher.childNodes[0];
if (child) {
// If the user pastes an image, the src attribute
// will represent the image as a base64 encoded string.
if (child.tagName === "IMG") {
getPngFromIMG(child, function(blob) {
// Clear the inner html to make sure we're always
// getting the latest inserted content
pasteCatcher.innerHTML = "";
// save the png blob in our list
files.push(blob);
createImage(URL.createObjectURL(blob));
});
}
}
}
function getPngFromIMG(img, callback) {
if (img.naturalWidth) // if already loaded
draw();
else
img.onload = draw;
function draw() {
var canvas = document.createElement('canvas');
canvas.width = img.naturalWidth;
canvas.height = img.naturalHeight;
canvas.getContext('2d').drawImage(img, 0, 0);
canvas.toBlob(callback);
}
}
/* Creates a new image from a given source */
function createImage(source) {
var pastedImage = new Image();
pastedImage.onload = function(e) {
loadImage.src = e.target.src;
}
pastedImage.src = source;
}
btn.onclick = function() {
console.log(files);
}
<textarea id="pasteArea" placeholder="Paste Image Here"></textarea>
<img id="loadImage" />
<button id="btn">do something with pasted files</button>

Display image from ID3 image data using javascript

I've tried all of the methods I could find in stackoverflow. This two are some of the most complete posts:
Display image from blob using javascript and websockets
How can you encode a string to Base64 in JavaScript?
I'm using cloudinary and id3js. First I upload the mp3 file to
cloudinary, then I request the file with Ajax through id3js. This
gives me all of the ID3 tags.
openUploadModal() {
cloudinary.openUploadWidget(window.cloudinaryOptions,
(errors, track) => {
if(!values(errors).length) {
id3(track[0].secure_url, (errs, tags) => {
this.setState({
title: tags.title,
audio_url: track[0].secure_url,
artist: tags.artist,
uploaded: true,
cover_photo: this.getImage(tags.v2.image)
});
});
}
});
}
And the image converter:
getImage(image) {
var arrayBuffer = image.data;
var bytes = new Uint8Array(arrayBuffer);
return "data:image/png;base64,"+btoa(unescape(encodeURIComponent(bytes)));
}
This is what the tags object looks like:
I then use the return value of getImage in the background-image attribute of a div. There are no errors in the console (not a bad request) but when opening the data:image/jpg;base64,... link there's only a little white square on the page.
How can I get a working url from the image object in the ID3 tags?

If image.data is an ArrayBuffer, you can use FileReader. FileReader load event is asynchronous, you cannot return the result from the function without using Promise, though you can use FileReaderSync() at Worker.
See also createImageBitmap alternative on Safari.
var reader = new FileReader();
reader.onload = function() {
// do stuff with `data URI` of `image.data`
console.log(reader.result);
}
reader.readAsDataURL(new Blob([image.data], {type:image.mime}));

javascript to read file selects a file but doesn't read it

My script selects a file... but doesn't read it. I've been banging my head on it but can't make it work. It's part of my studies, I'm a greenhorn and I'm lost.
function readBlob() {
var files = document.getElementById('files').files;
if (!files.length) {
alert('Please select a file!');
return;
var file = files[0];
var start = 0;
var stop = file.size;
var reader = new FileReader();
if (file.webkitSlice) {
var blob = file.webkitSlice(start, stop);
//Creates new blob if using google chrome
} else if (file.mozSlice) {
var blob = file.mozSlice(start, stop);
//Creates new blob if using mozilla firefox
}
//read the contents of the file in as text into the blob
reader.readAsText(blob);
reader.onloadend = function(evt) {
if (evt.target.readyState == FileReader.DONE) {
document.getElementById('byte_content').textContent =
evt.target.result;
}
};
}
}

Seems like a simple syntax error to me, but maybe just an error inserting it into stack overflow. The entire thing, the slicing of the file, the insertion into the document, everything, is inside of the if (!files.length) statement. Therefore, the script only executes when there is no file (catching on to the problem yet :) but it is actually meant to do the opposite. All of the important stuff is supposed to be outside of the if statement.

Get Base64 encode file-data from Input Form

I've got a basic HTML form from which I can grab a bit of information that I'm examining in Firebug.
My only issues is that I'm trying to base64 encode the file data before it's sent to the server where it's required to be in that form to be saved to the database.
<input type="file" id="fileupload" />
And in Javascript+jQuery:
var file = $('#fileupload').attr("files")[0];
I have some operations based on available javascript: .getAsBinary(), .getAsText(), .getAsTextURL
However none of these return usable text that can be inserted as they contain unusable 'characters' - I don't want to have a 'postback' occur in my file uploaded, and I need to have multiple forms targeting specific objects so it's important I get the file and use Javascript this way.
How should I get the file in such a way that I can use one of the Javascript base64 encoders that are widely available!?
Thanks
Update - Starting bounty here, need cross-browser support!!!
Here is where I'm at:
<input type="file" id="fileuploadform" />
<script type="text/javascript">
var uploadformid = 'fileuploadform';
var uploadform = document.getElementById(uploadformid);
/* method to fetch and encode specific file here based on different browsers */
</script>
Couple of issues with cross browser support:
var file = $j(fileUpload.toString()).attr('files')[0];
fileBody = file.getAsDataURL(); // only would works in Firefox
Also, IE doesn't support:
var file = $j(fileUpload.toString()).attr('files')[0];
So I have to replace with:
var element = 'id';
var element = document.getElementById(id);
For IE Support.
This works in Firefox, Chrome and, Safari (but doesn't properly encode the file, or at least after it's been posted the file doesn't come out right)
var file = $j(fileUpload.toString()).attr('files')[0];
var encoded = Btoa(file);
Also,
file.readAsArrayBuffer()
Seems to be only supported in HTML5?
Lots of people suggested: http://www.webtoolkit.info/javascript-base64.html
But this only returns an error on the UTF_8 method before it base64 encodes? (or an empty string)
var encoded = Base64.encode(file);

It's entirely possible in browser-side javascript.
The easy way:
The readAsDataURL() method might already encode it as base64 for you. You'll probably need to strip out the beginning stuff (up to the first ,), but that's no biggie. This would take all the fun out though.
The hard way:
If you want to try it the hard way (or it doesn't work), look at readAsArrayBuffer(). This will give you a Uint8Array and you can use the method specified. This is probably only useful if you want to mess with the data itself, such as manipulating image data or doing other voodoo magic before you upload.
There are two methods:
Convert to string and use the built-in btoa or similar
I haven't tested all cases, but works for me- just get the char-codes
Convert directly from a Uint8Array to base64
I recently implemented tar in the browser. As part of that process, I made my own direct Uint8Array->base64 implementation. I don't think you'll need that, but it's here if you want to take a look; it's pretty neat.
What I do now:
The code for converting to string from a Uint8Array is pretty simple (where buf is a Uint8Array):
function uint8ToString(buf) {
var i, length, out = '';
for (i = 0, length = buf.length; i < length; i += 1) {
out += String.fromCharCode(buf[i]);
}
return out;
}
From there, just do:
var base64 = btoa(uint8ToString(yourUint8Array));
Base64 will now be a base64-encoded string, and it should upload just peachy. Try this if you want to double check before pushing:
window.open("data:application/octet-stream;base64," + base64);
This will download it as a file.
Other info:
To get the data as a Uint8Array, look at the MDN docs:
https://developer.mozilla.org/en/DOM/FileReader

My solution was use readAsBinaryString() and btoa() on its result.
uploadFileToServer(event) {
var file = event.srcElement.files[0];
console.log(file);
var reader = new FileReader();
reader.readAsBinaryString(file);
reader.onload = function() {
console.log(btoa(reader.result));
};
reader.onerror = function() {
console.log('there are some problems');
};
}

I used FileReader to display image on click of the file upload button not using any Ajax requests. Following is the code hope it might help some one.
$(document).ready(function($) {
$.extend( true, jQuery.fn, {
imagePreview: function( options ){
var defaults = {};
if( options ){
$.extend( true, defaults, options );
}
$.each( this, function(){
var $this = $( this );
$this.bind( 'change', function( evt ){
var files = evt.target.files; // FileList object
// Loop through the FileList and render image files as thumbnails.
for (var i = 0, f; f = files[i]; i++) {
// Only process image files.
if (!f.type.match('image.*')) {
continue;
}
var reader = new FileReader();
// Closure to capture the file information.
reader.onload = (function(theFile) {
return function(e) {
// Render thumbnail.
$('#imageURL').attr('src',e.target.result);
};
})(f);
// Read in the image file as a data URL.
reader.readAsDataURL(f);
}
});
});
}
});
$( '#fileinput' ).imagePreview();
});

Inspired by #Josef's answer:
const fileToBase64 = async (file) =>
new Promise((resolve, reject) => {
const reader = new FileReader()
reader.readAsDataURL(file)
reader.onload = () => resolve(reader.result)
reader.onerror = (e) => reject(e)
})
const file = event.srcElement.files[0];
const imageStr = await fileToBase64(file)

Complete example
Html file input
<style>
.upload-button {
background-color: grey;
}
.upload-button input{
display:none;
}
</style>
<label for="upload-photo" class="upload-button">
Upload file
<input
type="file"
id="upload-photo"
</input>
</label>
JS Handler
document.getElementById("upload-photo").addEventListener("change", function({target}){
if (target.files && target.files.length) {
try {
const uploadedImageBase64 = await convertFileToBase64(target.files[0]);
//do something with above data string
} catch() {
//handle error
}
}
})
function convertFileToBase64(file) {
return new Promise((resolve, reject) => {
const reader = new FileReader();
reader.readAsDataURL(file);
reader.onload = () => resolve(reader.result);
// Typescript users: use following line
// reader.onload = () => resolve(reader.result as string);
reader.onerror = reject;
});
}

After struggling with this myself, I've come to implement FileReader for browsers that support it (Chrome, Firefox and the as-yet unreleased Safari 6), and a PHP script that echos back POSTed file data as Base64-encoded data for the other browsers.

So why dont you agree with user of the system to select an image from a known folder? Or they can set their choice folder for images.
Most browsers wont support full path but you can get the filename eg "image.png"
Using PHP inbuilt function to encode:
#$picture_base64 = base64_encode( file_get_contents($image_file_name) );
The sign # will suppress error if path is not found but the result will be a null for variable $picture_base64 so i guess youre ok with null like i am else do a check for null before proceeding.
In html you can select an image filename to the input e.g. "image.png" ( but not the full path)
<input type="file" name="image" id="image" >
Then in PHP you can do:
$path = "C:\\users\\john\\Desktop\\images\\"
#$picture_base64 = base64_encode( file_get_contents( $path. $_POST['image']);
Then $picture_base64 will be something like
"AQAAAAMAAAAHAAAADwAAAB8AAAA/AAAAfwAAAP8AAAD/AQAA/w"

I've started to think that using the 'iframe' for Ajax style upload might be a much better choice for my situation until HTML5 comes full circle and I don't have to support legacy browsers in my app!

Is it possible to save a File object in LocalStorage and then reload a File via FileReader when a user comes back to a page?

For example, say the user loads some very large images or media files in to your web app. When they return you want your app to show what they've previously loaded, but can't keep the actual file data in LocalStorage because the data is too large.

This is NOT possible with localStorage. Data stored in localStorage needs to be one of the primitive types that can be serializable. This does not include the File object.
For example, this will not work as you'd expect:
var el = document.createElement('input');
el.type='file';
el.onchange = function(e) {
localStorage.file = JSON.stringify(this.files[0]);
// LATER ON...
var reader = new FileReader();
reader.onload = function(e) {
var result = this.result; // never reaches here.
};
reader.readAsText(JSON.parse(localStorage.f));
};
document.body.appendChild(el);
The solution is to use a more powerful storage option like writing the file contents to the HTML5 Filesystem or stashing it in IndexedDB.

Technically you can if you just need to save small files in localStorage.
Just base64 that ish and since it's a string... it's localStorage-friendly.
I think localStorage has a ~5MB limit. base64 strings are pretty low file size so this is a feasible way to store small images. If you use this lazy man's way, the downside is you'll have to mind the 5MB limit. I think it could def be a solution depending on your needs.

Yes, this is possible. You can insert whatever information about the file you want into LocalStorage, provided you serialize it to one of the primitive types supported. You can also serialize the whole file into LocalStorage and retrieve that later if you want, but there are limitations on the size of the file depending on browser.
The following shows how to achieve this using two different approaches:
(function () {
// localStorage with image
var storageFiles = JSON.parse(localStorage.getItem("storageFiles")) || {},
elephant = document.getElementById("elephant"),
storageFilesDate = storageFiles.date,
date = new Date(),
todaysDate = (date.getMonth() + 1).toString() + date.getDate().toString();
// Compare date and create localStorage if it's not existing/too old
if (typeof storageFilesDate === "undefined" || storageFilesDate < todaysDate) {
// Take action when the image has loaded
elephant.addEventListener("load", function () {
var imgCanvas = document.createElement("canvas"),
imgContext = imgCanvas.getContext("2d");
// Make sure canvas is as big as the picture
imgCanvas.width = elephant.width;
imgCanvas.height = elephant.height;
// Draw image into canvas element
imgContext.drawImage(elephant, 0, 0, elephant.width, elephant.height);
// Save image as a data URL
storageFiles.elephant = imgCanvas.toDataURL("image/png");
// Set date for localStorage
storageFiles.date = todaysDate;
// Save as JSON in localStorage
try {
localStorage.setItem("storageFiles", JSON.stringify(storageFiles));
}
catch (e) {
console.log("Storage failed: " + e);
}
}, false);
// Set initial image src
elephant.setAttribute("src", "elephant.png");
}
else {
// Use image from localStorage
elephant.setAttribute("src", storageFiles.elephant);
}
// Getting a file through XMLHttpRequest as an arraybuffer and creating a Blob
var rhinoStorage = localStorage.getItem("rhino"),
rhino = document.getElementById("rhino");
if (rhinoStorage) {
// Reuse existing Data URL from localStorage
rhino.setAttribute("src", rhinoStorage);
}
else {
// Create XHR, BlobBuilder and FileReader objects
var xhr = new XMLHttpRequest(),
blob,
fileReader = new FileReader();
xhr.open("GET", "rhino.png", true);
// Set the responseType to arraybuffer. "blob" is an option too, rendering BlobBuilder unnecessary, but the support for "blob" is not widespread enough yet
xhr.responseType = "arraybuffer";
xhr.addEventListener("load", function () {
if (xhr.status === 200) {
// Create a blob from the response
blob = new Blob([xhr.response], {type: "image/png"});
// onload needed since Google Chrome doesn't support addEventListener for FileReader
fileReader.onload = function (evt) {
// Read out file contents as a Data URL
var result = evt.target.result;
// Set image src to Data URL
rhino.setAttribute("src", result);
// Store Data URL in localStorage
try {
localStorage.setItem("rhino", result);
}
catch (e) {
console.log("Storage failed: " + e);
}
};
// Load blob as Data URL
fileReader.readAsDataURL(blob);
}
}, false);
// Send XHR
xhr.send();
}
})();
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