Related
var profileImage = fileInputInByteArray;
$.ajax({
url: 'abc.com/',
type: 'POST',
dataType: 'json',
data: {
// Other data
ProfileImage: profileimage
// Other data
},
success: {
}
})
// Code in WebAPI
[HttpPost]
public HttpResponseMessage UpdateProfile([FromUri]UpdateProfileModel response) {
//...
return response;
}
public class UpdateProfileModel {
// ...
public byte[] ProfileImage {get ;set; }
// ...
}
<input type="file" id="inputFile" />
I am using ajax call to post byte[] value of a input type = file input to web api which receives in byte[] format. However, I am experiencing difficulty of getting byte array. I am expecting that we can get the byte array through File API.
Note: I need to store the byte array in a variable first before passing through ajax call
[Edit]
As noted in comments above, while still on some UA implementations, readAsBinaryString method didn't made its way to the specs and should not be used in production.
Instead, use readAsArrayBuffer and loop through it's buffer to get back the binary string :
document.querySelector('input').addEventListener('change', function() {
var reader = new FileReader();
reader.onload = function() {
var arrayBuffer = this.result,
array = new Uint8Array(arrayBuffer),
binaryString = String.fromCharCode.apply(null, array);
console.log(binaryString);
}
reader.readAsArrayBuffer(this.files[0]);
}, false);
<input type="file" />
<div id="result"></div>
For a more robust way to convert your arrayBuffer in binary string, you can refer to this answer.
[old answer] (modified)
Yes, the file API does provide a way to convert your File, in the <input type="file"/> to a binary string, thanks to the FileReader Object and its method readAsBinaryString.
[But don't use it in production !]
document.querySelector('input').addEventListener('change', function(){
var reader = new FileReader();
reader.onload = function(){
var binaryString = this.result;
document.querySelector('#result').innerHTML = binaryString;
}
reader.readAsBinaryString(this.files[0]);
}, false);
<input type="file"/>
<div id="result"></div>
If you want an array buffer, then you can use the readAsArrayBuffer() method :
document.querySelector('input').addEventListener('change', function(){
var reader = new FileReader();
reader.onload = function(){
var arrayBuffer = this.result;
console.log(arrayBuffer);
document.querySelector('#result').innerHTML = arrayBuffer + ' '+arrayBuffer.byteLength;
}
reader.readAsArrayBuffer(this.files[0]);
}, false);
<input type="file"/>
<div id="result"></div>
$(document).ready(function(){
(function (document) {
var input = document.getElementById("files"),
output = document.getElementById("result"),
fileData; // We need fileData to be visible to getBuffer.
// Eventhandler for file input.
function openfile(evt) {
var files = input.files;
// Pass the file to the blob, not the input[0].
fileData = new Blob([files[0]]);
// Pass getBuffer to promise.
var promise = new Promise(getBuffer);
// Wait for promise to be resolved, or log error.
promise.then(function(data) {
// Here you can pass the bytes to another function.
output.innerHTML = data.toString();
console.log(data);
}).catch(function(err) {
console.log('Error: ',err);
});
}
/*
Create a function which will be passed to the promise
and resolve it when FileReader has finished loading the file.
*/
function getBuffer(resolve) {
var reader = new FileReader();
reader.readAsArrayBuffer(fileData);
reader.onload = function() {
var arrayBuffer = reader.result
var bytes = new Uint8Array(arrayBuffer);
resolve(bytes);
}
}
// Eventlistener for file input.
input.addEventListener('change', openfile, false);
}(document));
});
<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
</head>
<body>
<input type="file" id="files"/>
<div id="result"></div>
</body>
</html>
Modern browsers now have the arrayBuffer method on Blob's:
document.querySelector('input').addEventListener('change', async (event) => {
const buffer = await event.target.files[0].arrayBuffer()
console.log(buffer)
}, false)
🎉 🎉
This is a long post, but I was tired of all these examples that weren't working for me because they used Promise objects or an errant this that has a different meaning when you are using Reactjs. My implementation was using a DropZone with reactjs, and I got the bytes using a framework similar to what is posted at this following site, when nothing else above would work: https://www.mokuji.me/article/drop-upload-tutorial-1 . There were 2 keys, for me:
You have to get the bytes from the event object, using and during a FileReader's onload function.
I tried various combinations, but in the end, what worked was:
const bytes = e.target.result.split('base64,')[1];
Where e is the event. React requires const, you could use var in plain Javascript. But that gave me the base64 encoded byte string.
So I'm just going to include the applicable lines for integrating this as if you were using React, because that's how I was building it, but try to also generalize this, and add comments where necessary, to make it applicable to a vanilla Javascript implementation - caveated that I did not use it like that in such a construct to test it.
These would be your bindings at the top, in your constructor, in a React framework (not relevant to a vanilla Javascript implementation):
this.uploadFile = this.uploadFile.bind(this);
this.processFile = this.processFile.bind(this);
this.errorHandler = this.errorHandler.bind(this);
this.progressHandler = this.progressHandler.bind(this);
And you'd have onDrop={this.uploadFile} in your DropZone element. If you were doing this without React, this is the equivalent of adding the onclick event handler you want to run when you click the "Upload File" button.
<button onclick="uploadFile(event);" value="Upload File" />
Then the function (applicable lines... I'll leave out my resetting my upload progress indicator, etc.):
uploadFile(event){
// This is for React, only
this.setState({
files: event,
});
console.log('File count: ' + this.state.files.length);
// You might check that the "event" has a file & assign it like this
// in vanilla Javascript:
// var files = event.target.files;
// if (!files && files.length > 0)
// files = (event.dataTransfer ? event.dataTransfer.files :
// event.originalEvent.dataTransfer.files);
// You cannot use "files" as a variable in React, however:
const in_files = this.state.files;
// iterate, if files length > 0
if (in_files.length > 0) {
for (let i = 0; i < in_files.length; i++) {
// use this, instead, for vanilla JS:
// for (var i = 0; i < files.length; i++) {
const a = i + 1;
console.log('in loop, pass: ' + a);
const f = in_files[i]; // or just files[i] in vanilla JS
const reader = new FileReader();
reader.onerror = this.errorHandler;
reader.onprogress = this.progressHandler;
reader.onload = this.processFile(f);
reader.readAsDataURL(f);
}
}
}
There was this question on that syntax, for vanilla JS, on how to get that file object:
JavaScript/HTML5/jQuery Drag-And-Drop Upload - "Uncaught TypeError: Cannot read property 'files' of undefined"
Note that React's DropZone will already put the File object into this.state.files for you, as long as you add files: [], to your this.state = { .... } in your constructor. I added syntax from an answer on that post on how to get your File object. It should work, or there are other posts there that can help. But all that Q/A told me was how to get the File object, not the blob data, itself. And even if I did fileData = new Blob([files[0]]); like in sebu's answer, which didn't include var with it for some reason, it didn't tell me how to read that blob's contents, and how to do it without a Promise object. So that's where the FileReader came in, though I actually tried and found I couldn't use their readAsArrayBuffer to any avail.
You will have to have the other functions that go along with this construct - one to handle onerror, one for onprogress (both shown farther below), and then the main one, onload, that actually does the work once a method on reader is invoked in that last line. Basically you are passing your event.dataTransfer.files[0] straight into that onload function, from what I can tell.
So the onload method calls my processFile() function (applicable lines, only):
processFile(theFile) {
return function(e) {
const bytes = e.target.result.split('base64,')[1];
}
}
And bytes should have the base64 bytes.
Additional functions:
errorHandler(e){
switch (e.target.error.code) {
case e.target.error.NOT_FOUND_ERR:
alert('File not found.');
break;
case e.target.error.NOT_READABLE_ERR:
alert('File is not readable.');
break;
case e.target.error.ABORT_ERR:
break; // no operation
default:
alert('An error occurred reading this file.');
break;
}
}
progressHandler(e) {
if (e.lengthComputable){
const loaded = Math.round((e.loaded / e.total) * 100);
let zeros = '';
// Percent loaded in string
if (loaded >= 0 && loaded < 10) {
zeros = '00';
}
else if (loaded < 100) {
zeros = '0';
}
// Display progress in 3-digits and increase bar length
document.getElementById("progress").textContent = zeros + loaded.toString();
document.getElementById("progressBar").style.width = loaded + '%';
}
}
And applicable progress indicator markup:
<table id="tblProgress">
<tbody>
<tr>
<td><b><span id="progress">000</span>%</b> <span className="progressBar"><span id="progressBar" /></span></td>
</tr>
</tbody>
</table>
And CSS:
.progressBar {
background-color: rgba(255, 255, 255, .1);
width: 100%;
height: 26px;
}
#progressBar {
background-color: rgba(87, 184, 208, .5);
content: '';
width: 0;
height: 26px;
}
EPILOGUE:
Inside processFile(), for some reason, I couldn't add bytes to a variable I carved out in this.state. So, instead, I set it directly to the variable, attachments, that was in my JSON object, RequestForm - the same object as my this.state was using. attachments is an array so I could push multiple files. It went like this:
const fileArray = [];
// Collect any existing attachments
if (RequestForm.state.attachments.length > 0) {
for (let i=0; i < RequestForm.state.attachments.length; i++) {
fileArray.push(RequestForm.state.attachments[i]);
}
}
// Add the new one to this.state
fileArray.push(bytes);
// Update the state
RequestForm.setState({
attachments: fileArray,
});
Then, because this.state already contained RequestForm:
this.stores = [
RequestForm,
]
I could reference it as this.state.attachments from there on out. React feature that isn't applicable in vanilla JS. You could build a similar construct in plain JavaScript with a global variable, and push, accordingly, however, much easier:
var fileArray = new Array(); // place at the top, before any functions
// Within your processFile():
var newFileArray = [];
if (fileArray.length > 0) {
for (var i=0; i < fileArray.length; i++) {
newFileArray.push(fileArray[i]);
}
}
// Add the new one
newFileArray.push(bytes);
// Now update the global variable
fileArray = newFileArray;
Then you always just reference fileArray, enumerate it for any file byte strings, e.g. var myBytes = fileArray[0]; for the first file.
This is simple way to convert files to Base64 and avoid "maximum call stack size exceeded at FileReader.reader.onload" with the file has big size.
document.querySelector('#fileInput').addEventListener('change', function () {
var reader = new FileReader();
var selectedFile = this.files[0];
reader.onload = function () {
var comma = this.result.indexOf(',');
var base64 = this.result.substr(comma + 1);
console.log(base64);
}
reader.readAsDataURL(selectedFile);
}, false);
<input id="fileInput" type="file" />
document.querySelector('input').addEventListener('change', function(){
var reader = new FileReader();
reader.onload = function(){
var arrayBuffer = this.result,
array = new Uint8Array(arrayBuffer),
binaryString = String.fromCharCode.apply(null, array);
console.log(binaryString);
console.log(arrayBuffer);
document.querySelector('#result').innerHTML = arrayBuffer + ' '+arrayBuffer.byteLength;
}
reader.readAsArrayBuffer(this.files[0]);
}, false);
<input type="file"/>
<div id="result"></div>
Here is one answer to get the actual final byte array , just using FileReader and ArrayBuffer :
const test_function = async () => {
... ... ...
const get_file_array = (file) => {
return new Promise((acc, err) => {
const reader = new FileReader();
reader.onload = (event) => { acc(event.target.result) };
reader.onerror = (err) => { err(err) };
reader.readAsArrayBuffer(file);
});
}
const temp = await get_file_array(files[0])
console.log('here we finally ve the file as a ArrayBuffer : ',temp);
const fileb = new Uint8Array(fileb)
... ... ...
}
where file is directly the File object u want to read , this has to be done in a async function...
var profileImage = fileInputInByteArray;
$.ajax({
url: 'abc.com/',
type: 'POST',
dataType: 'json',
data: {
// Other data
ProfileImage: profileimage
// Other data
},
success: {
}
})
// Code in WebAPI
[HttpPost]
public HttpResponseMessage UpdateProfile([FromUri]UpdateProfileModel response) {
//...
return response;
}
public class UpdateProfileModel {
// ...
public byte[] ProfileImage {get ;set; }
// ...
}
<input type="file" id="inputFile" />
I am using ajax call to post byte[] value of a input type = file input to web api which receives in byte[] format. However, I am experiencing difficulty of getting byte array. I am expecting that we can get the byte array through File API.
Note: I need to store the byte array in a variable first before passing through ajax call
[Edit]
As noted in comments above, while still on some UA implementations, readAsBinaryString method didn't made its way to the specs and should not be used in production.
Instead, use readAsArrayBuffer and loop through it's buffer to get back the binary string :
document.querySelector('input').addEventListener('change', function() {
var reader = new FileReader();
reader.onload = function() {
var arrayBuffer = this.result,
array = new Uint8Array(arrayBuffer),
binaryString = String.fromCharCode.apply(null, array);
console.log(binaryString);
}
reader.readAsArrayBuffer(this.files[0]);
}, false);
<input type="file" />
<div id="result"></div>
For a more robust way to convert your arrayBuffer in binary string, you can refer to this answer.
[old answer] (modified)
Yes, the file API does provide a way to convert your File, in the <input type="file"/> to a binary string, thanks to the FileReader Object and its method readAsBinaryString.
[But don't use it in production !]
document.querySelector('input').addEventListener('change', function(){
var reader = new FileReader();
reader.onload = function(){
var binaryString = this.result;
document.querySelector('#result').innerHTML = binaryString;
}
reader.readAsBinaryString(this.files[0]);
}, false);
<input type="file"/>
<div id="result"></div>
If you want an array buffer, then you can use the readAsArrayBuffer() method :
document.querySelector('input').addEventListener('change', function(){
var reader = new FileReader();
reader.onload = function(){
var arrayBuffer = this.result;
console.log(arrayBuffer);
document.querySelector('#result').innerHTML = arrayBuffer + ' '+arrayBuffer.byteLength;
}
reader.readAsArrayBuffer(this.files[0]);
}, false);
<input type="file"/>
<div id="result"></div>
$(document).ready(function(){
(function (document) {
var input = document.getElementById("files"),
output = document.getElementById("result"),
fileData; // We need fileData to be visible to getBuffer.
// Eventhandler for file input.
function openfile(evt) {
var files = input.files;
// Pass the file to the blob, not the input[0].
fileData = new Blob([files[0]]);
// Pass getBuffer to promise.
var promise = new Promise(getBuffer);
// Wait for promise to be resolved, or log error.
promise.then(function(data) {
// Here you can pass the bytes to another function.
output.innerHTML = data.toString();
console.log(data);
}).catch(function(err) {
console.log('Error: ',err);
});
}
/*
Create a function which will be passed to the promise
and resolve it when FileReader has finished loading the file.
*/
function getBuffer(resolve) {
var reader = new FileReader();
reader.readAsArrayBuffer(fileData);
reader.onload = function() {
var arrayBuffer = reader.result
var bytes = new Uint8Array(arrayBuffer);
resolve(bytes);
}
}
// Eventlistener for file input.
input.addEventListener('change', openfile, false);
}(document));
});
<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
</head>
<body>
<input type="file" id="files"/>
<div id="result"></div>
</body>
</html>
Modern browsers now have the arrayBuffer method on Blob's:
document.querySelector('input').addEventListener('change', async (event) => {
const buffer = await event.target.files[0].arrayBuffer()
console.log(buffer)
}, false)
🎉 🎉
This is a long post, but I was tired of all these examples that weren't working for me because they used Promise objects or an errant this that has a different meaning when you are using Reactjs. My implementation was using a DropZone with reactjs, and I got the bytes using a framework similar to what is posted at this following site, when nothing else above would work: https://www.mokuji.me/article/drop-upload-tutorial-1 . There were 2 keys, for me:
You have to get the bytes from the event object, using and during a FileReader's onload function.
I tried various combinations, but in the end, what worked was:
const bytes = e.target.result.split('base64,')[1];
Where e is the event. React requires const, you could use var in plain Javascript. But that gave me the base64 encoded byte string.
So I'm just going to include the applicable lines for integrating this as if you were using React, because that's how I was building it, but try to also generalize this, and add comments where necessary, to make it applicable to a vanilla Javascript implementation - caveated that I did not use it like that in such a construct to test it.
These would be your bindings at the top, in your constructor, in a React framework (not relevant to a vanilla Javascript implementation):
this.uploadFile = this.uploadFile.bind(this);
this.processFile = this.processFile.bind(this);
this.errorHandler = this.errorHandler.bind(this);
this.progressHandler = this.progressHandler.bind(this);
And you'd have onDrop={this.uploadFile} in your DropZone element. If you were doing this without React, this is the equivalent of adding the onclick event handler you want to run when you click the "Upload File" button.
<button onclick="uploadFile(event);" value="Upload File" />
Then the function (applicable lines... I'll leave out my resetting my upload progress indicator, etc.):
uploadFile(event){
// This is for React, only
this.setState({
files: event,
});
console.log('File count: ' + this.state.files.length);
// You might check that the "event" has a file & assign it like this
// in vanilla Javascript:
// var files = event.target.files;
// if (!files && files.length > 0)
// files = (event.dataTransfer ? event.dataTransfer.files :
// event.originalEvent.dataTransfer.files);
// You cannot use "files" as a variable in React, however:
const in_files = this.state.files;
// iterate, if files length > 0
if (in_files.length > 0) {
for (let i = 0; i < in_files.length; i++) {
// use this, instead, for vanilla JS:
// for (var i = 0; i < files.length; i++) {
const a = i + 1;
console.log('in loop, pass: ' + a);
const f = in_files[i]; // or just files[i] in vanilla JS
const reader = new FileReader();
reader.onerror = this.errorHandler;
reader.onprogress = this.progressHandler;
reader.onload = this.processFile(f);
reader.readAsDataURL(f);
}
}
}
There was this question on that syntax, for vanilla JS, on how to get that file object:
JavaScript/HTML5/jQuery Drag-And-Drop Upload - "Uncaught TypeError: Cannot read property 'files' of undefined"
Note that React's DropZone will already put the File object into this.state.files for you, as long as you add files: [], to your this.state = { .... } in your constructor. I added syntax from an answer on that post on how to get your File object. It should work, or there are other posts there that can help. But all that Q/A told me was how to get the File object, not the blob data, itself. And even if I did fileData = new Blob([files[0]]); like in sebu's answer, which didn't include var with it for some reason, it didn't tell me how to read that blob's contents, and how to do it without a Promise object. So that's where the FileReader came in, though I actually tried and found I couldn't use their readAsArrayBuffer to any avail.
You will have to have the other functions that go along with this construct - one to handle onerror, one for onprogress (both shown farther below), and then the main one, onload, that actually does the work once a method on reader is invoked in that last line. Basically you are passing your event.dataTransfer.files[0] straight into that onload function, from what I can tell.
So the onload method calls my processFile() function (applicable lines, only):
processFile(theFile) {
return function(e) {
const bytes = e.target.result.split('base64,')[1];
}
}
And bytes should have the base64 bytes.
Additional functions:
errorHandler(e){
switch (e.target.error.code) {
case e.target.error.NOT_FOUND_ERR:
alert('File not found.');
break;
case e.target.error.NOT_READABLE_ERR:
alert('File is not readable.');
break;
case e.target.error.ABORT_ERR:
break; // no operation
default:
alert('An error occurred reading this file.');
break;
}
}
progressHandler(e) {
if (e.lengthComputable){
const loaded = Math.round((e.loaded / e.total) * 100);
let zeros = '';
// Percent loaded in string
if (loaded >= 0 && loaded < 10) {
zeros = '00';
}
else if (loaded < 100) {
zeros = '0';
}
// Display progress in 3-digits and increase bar length
document.getElementById("progress").textContent = zeros + loaded.toString();
document.getElementById("progressBar").style.width = loaded + '%';
}
}
And applicable progress indicator markup:
<table id="tblProgress">
<tbody>
<tr>
<td><b><span id="progress">000</span>%</b> <span className="progressBar"><span id="progressBar" /></span></td>
</tr>
</tbody>
</table>
And CSS:
.progressBar {
background-color: rgba(255, 255, 255, .1);
width: 100%;
height: 26px;
}
#progressBar {
background-color: rgba(87, 184, 208, .5);
content: '';
width: 0;
height: 26px;
}
EPILOGUE:
Inside processFile(), for some reason, I couldn't add bytes to a variable I carved out in this.state. So, instead, I set it directly to the variable, attachments, that was in my JSON object, RequestForm - the same object as my this.state was using. attachments is an array so I could push multiple files. It went like this:
const fileArray = [];
// Collect any existing attachments
if (RequestForm.state.attachments.length > 0) {
for (let i=0; i < RequestForm.state.attachments.length; i++) {
fileArray.push(RequestForm.state.attachments[i]);
}
}
// Add the new one to this.state
fileArray.push(bytes);
// Update the state
RequestForm.setState({
attachments: fileArray,
});
Then, because this.state already contained RequestForm:
this.stores = [
RequestForm,
]
I could reference it as this.state.attachments from there on out. React feature that isn't applicable in vanilla JS. You could build a similar construct in plain JavaScript with a global variable, and push, accordingly, however, much easier:
var fileArray = new Array(); // place at the top, before any functions
// Within your processFile():
var newFileArray = [];
if (fileArray.length > 0) {
for (var i=0; i < fileArray.length; i++) {
newFileArray.push(fileArray[i]);
}
}
// Add the new one
newFileArray.push(bytes);
// Now update the global variable
fileArray = newFileArray;
Then you always just reference fileArray, enumerate it for any file byte strings, e.g. var myBytes = fileArray[0]; for the first file.
This is simple way to convert files to Base64 and avoid "maximum call stack size exceeded at FileReader.reader.onload" with the file has big size.
document.querySelector('#fileInput').addEventListener('change', function () {
var reader = new FileReader();
var selectedFile = this.files[0];
reader.onload = function () {
var comma = this.result.indexOf(',');
var base64 = this.result.substr(comma + 1);
console.log(base64);
}
reader.readAsDataURL(selectedFile);
}, false);
<input id="fileInput" type="file" />
document.querySelector('input').addEventListener('change', function(){
var reader = new FileReader();
reader.onload = function(){
var arrayBuffer = this.result,
array = new Uint8Array(arrayBuffer),
binaryString = String.fromCharCode.apply(null, array);
console.log(binaryString);
console.log(arrayBuffer);
document.querySelector('#result').innerHTML = arrayBuffer + ' '+arrayBuffer.byteLength;
}
reader.readAsArrayBuffer(this.files[0]);
}, false);
<input type="file"/>
<div id="result"></div>
Here is one answer to get the actual final byte array , just using FileReader and ArrayBuffer :
const test_function = async () => {
... ... ...
const get_file_array = (file) => {
return new Promise((acc, err) => {
const reader = new FileReader();
reader.onload = (event) => { acc(event.target.result) };
reader.onerror = (err) => { err(err) };
reader.readAsArrayBuffer(file);
});
}
const temp = await get_file_array(files[0])
console.log('here we finally ve the file as a ArrayBuffer : ',temp);
const fileb = new Uint8Array(fileb)
... ... ...
}
where file is directly the File object u want to read , this has to be done in a async function...
I have read this and this questions which seems to suggest that the file MIME type could be checked using JavaScript on client side. Now, I understand that the real validation still has to be done on server side. I want to perform a client side checking to avoid unnecessary wastage of server resource.
To test whether this can be done on client side, I changed the extension of a JPEG test file to .png and choose the file for upload. Before sending the file, I query the file object using a JavaScript console:
document.getElementsByTagName('input')[0].files[0];
This is what I get on Chrome 28.0:
File {webkitRelativePath: "", lastModifiedDate: Tue Oct 16 2012
10:00:00 GMT+0000 (UTC), name: "test.png", type: "image/png", size:
500055…}
It shows type to be image/png which seems to indicate that the checking is done based on file extension instead of MIME type. I tried Firefox 22.0 and it gives me the same result. But according to the W3C spec, MIME Sniffing should be implemented.
Am I right to say that there is no way to check the MIME type with JavaScript at the moment? Or am I missing something?
You can easily determine the file MIME type with JavaScript's FileReader before uploading it to a server. I agree that we should prefer server-side checking over client-side, but client-side checking is still possible. I'll show you how and provide a working demo at the bottom.
Check that your browser supports both File and Blob. All major ones should.
if (window.FileReader && window.Blob) {
// All the File APIs are supported.
} else {
// File and Blob are not supported
}
Step 1:
You can retrieve the File information from an <input> element like this (ref):
<input type="file" id="your-files" multiple>
<script>
var control = document.getElementById("your-files");
control.addEventListener("change", function(event) {
// When the control has changed, there are new files
var files = control.files,
for (var i = 0; i < files.length; i++) {
console.log("Filename: " + files[i].name);
console.log("Type: " + files[i].type);
console.log("Size: " + files[i].size + " bytes");
}
}, false);
</script>
Here is a drag-and-drop version of the above (ref):
<div id="your-files"></div>
<script>
var target = document.getElementById("your-files");
target.addEventListener("dragover", function(event) {
event.preventDefault();
}, false);
target.addEventListener("drop", function(event) {
// Cancel default actions
event.preventDefault();
var files = event.dataTransfer.files,
for (var i = 0; i < files.length; i++) {
console.log("Filename: " + files[i].name);
console.log("Type: " + files[i].type);
console.log("Size: " + files[i].size + " bytes");
}
}, false);
</script>
Step 2:
We can now inspect the files and tease out headers and MIME types.
✘ Quick method
You can naïvely ask Blob for the MIME type of whatever file it represents using this pattern:
var blob = files[i]; // See step 1 above
console.log(blob.type);
For images, MIME types come back like the following:
image/jpeg
image/png
...
Caveat: The MIME type is detected from the file extension and can be fooled or spoofed. One can rename a .jpg to a .png and the MIME type will be be reported as image/png.
✓ Proper header-inspecting method
To get the bonafide MIME type of a client-side file we can go a step further and inspect the first few bytes of the given file to compare against so-called magic numbers. Be warned that it's not entirely straightforward because, for instance, JPEG has a few "magic numbers". This is because the format has evolved since 1991. You might get away with checking only the first two bytes, but I prefer checking at least 4 bytes to reduce false positives.
Example file signatures of JPEG (first 4 bytes):
FF D8 FF E0 (SOI + ADD0)
FF D8 FF E1 (SOI + ADD1)
FF D8 FF E2 (SOI + ADD2)
Here is the essential code to retrieve the file header:
var blob = files[i]; // See step 1 above
var fileReader = new FileReader();
fileReader.onloadend = function(e) {
var arr = (new Uint8Array(e.target.result)).subarray(0, 4);
var header = "";
for(var i = 0; i < arr.length; i++) {
header += arr[i].toString(16);
}
console.log(header);
// Check the file signature against known types
};
fileReader.readAsArrayBuffer(blob);
You can then determine the real MIME type like so (more file signatures here and here):
switch (header) {
case "89504e47":
type = "image/png";
break;
case "47494638":
type = "image/gif";
break;
case "ffd8ffe0":
case "ffd8ffe1":
case "ffd8ffe2":
case "ffd8ffe3":
case "ffd8ffe8":
type = "image/jpeg";
break;
default:
type = "unknown"; // Or you can use the blob.type as fallback
break;
}
Accept or reject file uploads as you like based on the MIME types expected.
Demo
Here is a working demo for local files and remote files (I had to bypass CORS just for this demo). Open the snippet, run it, and you should see three remote images of different types displayed. At the top you can select a local image or data file, and the file signature and/or MIME type will be displayed.
Notice that even if an image is renamed, its true MIME type can be determined. See below.
Screenshot
// Return the first few bytes of the file as a hex string
function getBLOBFileHeader(url, blob, callback) {
var fileReader = new FileReader();
fileReader.onloadend = function(e) {
var arr = (new Uint8Array(e.target.result)).subarray(0, 4);
var header = "";
for (var i = 0; i < arr.length; i++) {
header += arr[i].toString(16);
}
callback(url, header);
};
fileReader.readAsArrayBuffer(blob);
}
function getRemoteFileHeader(url, callback) {
var xhr = new XMLHttpRequest();
// Bypass CORS for this demo - naughty, Drakes
xhr.open('GET', '//cors-anywhere.herokuapp.com/' + url);
xhr.responseType = "blob";
xhr.onload = function() {
callback(url, xhr.response);
};
xhr.onerror = function() {
alert('A network error occurred!');
};
xhr.send();
}
function headerCallback(url, headerString) {
printHeaderInfo(url, headerString);
}
function remoteCallback(url, blob) {
printImage(blob);
getBLOBFileHeader(url, blob, headerCallback);
}
function printImage(blob) {
// Add this image to the document body for proof of GET success
var fr = new FileReader();
fr.onloadend = function() {
$("hr").after($("<img>").attr("src", fr.result))
.after($("<div>").text("Blob MIME type: " + blob.type));
};
fr.readAsDataURL(blob);
}
// Add more from http://en.wikipedia.org/wiki/List_of_file_signatures
function mimeType(headerString) {
switch (headerString) {
case "89504e47":
type = "image/png";
break;
case "47494638":
type = "image/gif";
break;
case "ffd8ffe0":
case "ffd8ffe1":
case "ffd8ffe2":
type = "image/jpeg";
break;
default:
type = "unknown";
break;
}
return type;
}
function printHeaderInfo(url, headerString) {
$("hr").after($("<div>").text("Real MIME type: " + mimeType(headerString)))
.after($("<div>").text("File header: 0x" + headerString))
.after($("<div>").text(url));
}
/* Demo driver code */
var imageURLsArray = ["http://media2.giphy.com/media/8KrhxtEsrdhD2/giphy.gif", "http://upload.wikimedia.org/wikipedia/commons/e/e9/Felis_silvestris_silvestris_small_gradual_decrease_of_quality.png", "http://static.giantbomb.com/uploads/scale_small/0/316/520157-apple_logo_dec07.jpg"];
// Check for FileReader support
if (window.FileReader && window.Blob) {
// Load all the remote images from the urls array
for (var i = 0; i < imageURLsArray.length; i++) {
getRemoteFileHeader(imageURLsArray[i], remoteCallback);
}
/* Handle local files */
$("input").on('change', function(event) {
var file = event.target.files[0];
if (file.size >= 2 * 1024 * 1024) {
alert("File size must be at most 2MB");
return;
}
remoteCallback(escape(file.name), file);
});
} else {
// File and Blob are not supported
$("hr").after( $("<div>").text("It seems your browser doesn't support FileReader") );
} /* Drakes, 2015 */
img {
max-height: 200px
}
div {
height: 26px;
font: Arial;
font-size: 12pt
}
form {
height: 40px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<form>
<input type="file" />
<div>Choose an image to see its file signature.</div>
</form>
<hr/>
As stated in other answers, you can check the mime type by checking the signature of the file in the first bytes of the file.
But what other answers are doing is loading the entire file in memory in order to check the signature, which is very wasteful and could easily freeze your browser if you select a big file by accident or not.
/**
* Load the mime type based on the signature of the first bytes of the file
* #param {File} file A instance of File
* #param {Function} callback Callback with the result
* #author Victor www.vitim.us
* #date 2017-03-23
*/
function loadMime(file, callback) {
//List of known mimes
var mimes = [
{
mime: 'image/jpeg',
pattern: [0xFF, 0xD8, 0xFF],
mask: [0xFF, 0xFF, 0xFF],
},
{
mime: 'image/png',
pattern: [0x89, 0x50, 0x4E, 0x47],
mask: [0xFF, 0xFF, 0xFF, 0xFF],
}
// you can expand this list #see https://mimesniff.spec.whatwg.org/#matching-an-image-type-pattern
];
function check(bytes, mime) {
for (var i = 0, l = mime.mask.length; i < l; ++i) {
if ((bytes[i] & mime.mask[i]) - mime.pattern[i] !== 0) {
return false;
}
}
return true;
}
var blob = file.slice(0, 4); //read the first 4 bytes of the file
var reader = new FileReader();
reader.onloadend = function(e) {
if (e.target.readyState === FileReader.DONE) {
var bytes = new Uint8Array(e.target.result);
for (var i=0, l = mimes.length; i<l; ++i) {
if (check(bytes, mimes[i])) return callback("Mime: " + mimes[i].mime + " <br> Browser:" + file.type);
}
return callback("Mime: unknown <br> Browser:" + file.type);
}
};
reader.readAsArrayBuffer(blob);
}
//when selecting a file on the input
fileInput.onchange = function() {
loadMime(fileInput.files[0], function(mime) {
//print the output to the screen
output.innerHTML = mime;
});
};
<input type="file" id="fileInput">
<div id="output"></div>
For anyone who's looking to not implement this themselves, Sindresorhus has created a utility that works in the browser and has the header-to-mime mappings for most documents you could want.
https://github.com/sindresorhus/file-type
You could combine Vitim.us's suggestion of only reading in the first X bytes to avoid loading everything into memory with using this utility (example in es6):
import fileType from 'file-type'; // or wherever you load the dependency
const blob = file.slice(0, fileType.minimumBytes);
const reader = new FileReader();
reader.onloadend = function(e) {
if (e.target.readyState !== FileReader.DONE) {
return;
}
const bytes = new Uint8Array(e.target.result);
const { ext, mime } = fileType.fromBuffer(bytes);
// ext is the desired extension and mime is the mimetype
};
reader.readAsArrayBuffer(blob);
Here is a Typescript implementation that supports webp.
This is based on the JavaScript answer by Vitim.us.
interface Mime {
mime: string;
pattern: (number | undefined)[];
}
// tslint:disable number-literal-format
// tslint:disable no-magic-numbers
const imageMimes: Mime[] = [
{
mime: 'image/png',
pattern: [0x89, 0x50, 0x4e, 0x47]
},
{
mime: 'image/jpeg',
pattern: [0xff, 0xd8, 0xff]
},
{
mime: 'image/gif',
pattern: [0x47, 0x49, 0x46, 0x38]
},
{
mime: 'image/webp',
pattern: [0x52, 0x49, 0x46, 0x46, undefined, undefined, undefined, undefined, 0x57, 0x45, 0x42, 0x50, 0x56, 0x50],
}
// You can expand this list #see https://mimesniff.spec.whatwg.org/#matching-an-image-type-pattern
];
// tslint:enable no-magic-numbers
// tslint:enable number-literal-format
function isMime(bytes: Uint8Array, mime: Mime): boolean {
return mime.pattern.every((p, i) => !p || bytes[i] === p);
}
function validateImageMimeType(file: File, callback: (b: boolean) => void) {
const numBytesNeeded = Math.max(...imageMimes.map(m => m.pattern.length));
const blob = file.slice(0, numBytesNeeded); // Read the needed bytes of the file
const fileReader = new FileReader();
fileReader.onloadend = e => {
if (!e || !fileReader.result) return;
const bytes = new Uint8Array(fileReader.result as ArrayBuffer);
const valid = imageMimes.some(mime => isMime(bytes, mime));
callback(valid);
};
fileReader.readAsArrayBuffer(blob);
}
// When selecting a file on the input
fileInput.onchange = () => {
const file = fileInput.files && fileInput.files[0];
if (!file) return;
validateImageMimeType(file, valid => {
if (!valid) {
alert('Not a valid image file.');
}
});
};
<input type="file" id="fileInput">
If you just want to check if the file uploaded is an image you can just try to load it into <img> tag an check for any error callback.
Example:
var input = document.getElementsByTagName('input')[0];
var reader = new FileReader();
reader.onload = function (e) {
imageExists(e.target.result, function(exists){
if (exists) {
// Do something with the image file..
} else {
// different file format
}
});
};
reader.readAsDataURL(input.files[0]);
function imageExists(url, callback) {
var img = new Image();
img.onload = function() { callback(true); };
img.onerror = function() { callback(false); };
img.src = url;
}
This is what you have to do
var fileVariable =document.getElementsById('fileId').files[0];
If you want to check for image file types then
if(fileVariable.type.match('image.*'))
{
alert('its an image');
}
As Drake states this could be done with FileReader. However, what I present here is a functional version. Take in consideration that the big problem with doing this with JavaScript is to reset the input file. Well, this restricts to only JPG (for other formats you will have to change the mime type and the magic number):
<form id="form-id">
<input type="file" id="input-id" accept="image/jpeg"/>
</form>
<script type="text/javascript">
$(function(){
$("#input-id").on('change', function(event) {
var file = event.target.files[0];
if(file.size>=2*1024*1024) {
alert("JPG images of maximum 2MB");
$("#form-id").get(0).reset(); //the tricky part is to "empty" the input file here I reset the form.
return;
}
if(!file.type.match('image/jp.*')) {
alert("only JPG images");
$("#form-id").get(0).reset(); //the tricky part is to "empty" the input file here I reset the form.
return;
}
var fileReader = new FileReader();
fileReader.onload = function(e) {
var int32View = new Uint8Array(e.target.result);
//verify the magic number
// for JPG is 0xFF 0xD8 0xFF 0xE0 (see https://en.wikipedia.org/wiki/List_of_file_signatures)
if(int32View.length>4 && int32View[0]==0xFF && int32View[1]==0xD8 && int32View[2]==0xFF && int32View[3]==0xE0) {
alert("ok!");
} else {
alert("only valid JPG images");
$("#form-id").get(0).reset(); //the tricky part is to "empty" the input file here I reset the form.
return;
}
};
fileReader.readAsArrayBuffer(file);
});
});
</script>
Take in consideration that this was tested on latest versions of Firefox and Chrome, and on IExplore 10.
For a complete list of mime types see Wikipedia.
For a complete list of magic number see Wikipedia.
I needed to check for a few more file types.
Following up the excellent answer given by Drakes, I came up with the below code after I found this website with a very extensive table of file types and their headers. Both in Hex and String.
I also needed an asynchronous function to deal with many files and other problems related to the project I'm working that does not matter here.
Here is the code in vanilla javascript.
// getFileMimeType
// #param {Object} the file object created by the input[type=file] DOM element.
// #return {Object} a Promise that resolves with the MIME type as argument or undefined
// if no MIME type matches were found.
const getFileMimeType = file => {
// Making the function async.
return new Promise(resolve => {
let fileReader = new FileReader();
fileReader.onloadend = event => {
const byteArray = new Uint8Array(event.target.result);
// Checking if it's JPEG. For JPEG we need to check the first 2 bytes.
// We can check further if more specific type is needed.
if(byteArray[0] == 255 && byteArray[1] == 216){
resolve('image/jpeg');
return;
}
// If it's not JPEG we can check for signature strings directly.
// This is only the case when the bytes have a readable character.
const td = new TextDecoder("utf-8");
const headerString = td.decode(byteArray);
// Array to be iterated [<string signature>, <MIME type>]
const mimeTypes = [
// Images
['PNG', 'image/png'],
// Audio
['ID3', 'audio/mpeg'],// MP3
// Video
['ftypmp4', 'video/mp4'],// MP4
['ftypisom', 'video/mp4'],// MP4
// HTML
['<!DOCTYPE html>', 'text/html'],
// PDF
['%PDF', 'application/pdf']
// Add the needed files for your case.
];
// Iterate over the required types.
for(let i = 0;i < mimeTypes.length;i++){
// If a type matches we return the MIME type
if(headerString.indexOf(mimeTypes[i][0]) > -1){
resolve(mimeTypes[i][1]);
return;
}
}
// If not is found we resolve with a blank argument
resolve();
}
// Slice enough bytes to get readable strings.
// I chose 32 arbitrarily. Note that some headers are offset by
// a number of bytes.
fileReader.readAsArrayBuffer(file.slice(0,32));
});
};
// The input[type=file] DOM element.
const fileField = document.querySelector('#file-upload');
// Event to detect when the user added files.
fileField.onchange = event => {
// We iterate over each file and log the file name and it's MIME type.
// This iteration is asynchronous.
Array.from(fileField.files, async file => {
console.log(file.name, await getFileMimeType(file));
});
};
Notice that in the getFileMimeType function you can employ 2 approaches to find the correct MIME type.
Search the bytes directly.
Search for Strings after converting the bytes to string.
I used the first approach with JPEG because what makes it identifiable are the first 2 bytes and those bytes are not readable string characters.
With the rest of the file types I could check for readable string character signatures. For example:
[video/mp4] -> 'ftypmp4' or 'ftypisom'
If you need to support a file that is not on the Gary Kessler's list, you can console.log() the bytes or converted string to find a proper signature for the obscure file you need to support.
Note1: The Gary Kessler's list has been updated and the mp4 signatures are different now, you should check it when implementing this.
Note2: the Array.from is designed to use a .map like function as it second argument.
Here's a minimal typescript/promise util for the browser;
export const getFileHeader = (file: File): Promise<string> => {
return new Promise(resolve => {
const headerBytes = file.slice(0, 4); // Read the first 4 bytes of the file
const fileReader = new FileReader();
fileReader.onloadend = (e: ProgressEvent<FileReader>) => {
const arr = new Uint8Array(e?.target?.result as ArrayBufferLike).subarray(
0,
4,
);
let header = '';
for (let i = 0; i < arr.length; i++) {
header += arr[i].toString(16);
}
resolve(header);
};
fileReader.readAsArrayBuffer(headerBytes);
});
};
Use like so in your validation (I needed a PDF check);
// https://mimesniff.spec.whatwg.org/#matching-an-image-type-pattern
const pdfBytePattern = "25504446"
const fileHeader = await getFileHeader(file)
const isPdf = fileHeader === pdfBytePattern // => true
Here is an extension of Roberto14's answer that does the following:
THIS WILL ONLY ALLOW IMAGES
Checks if FileReader is available and falls back to extension checking if it is not available.
Gives an error alert if not an image
If it is an image it loads a preview
** You should still do server side validation, this is more a convenience for the end user than anything else. But it is handy!
<form id="myform">
<input type="file" id="myimage" onchange="readURL(this)" />
<img id="preview" src="#" alt="Image Preview" />
</form>
<script>
function readURL(input) {
if (window.FileReader && window.Blob) {
if (input.files && input.files[0]) {
var reader = new FileReader();
reader.onload = function (e) {
var img = new Image();
img.onload = function() {
var preview = document.getElementById('preview');
preview.src = e.target.result;
};
img.onerror = function() {
alert('error');
input.value = '';
};
img.src = e.target.result;
}
reader.readAsDataURL(input.files[0]);
}
}
else {
var ext = input.value.split('.');
ext = ext[ext.length-1].toLowerCase();
var arrayExtensions = ['jpg' , 'jpeg', 'png', 'bmp', 'gif'];
if (arrayExtensions.lastIndexOf(ext) == -1) {
alert('error');
input.value = '';
}
else {
var preview = document.getElementById('preview');
preview.setAttribute('alt', 'Browser does not support preview.');
}
}
}
</script>
For Png files you can do even more checking than just checking for some magic header bytes, as Png files have a particular file format that you can check.
TLDR: there are a series of chunks that must be in a specific order, and each chunk has a crc error correction code that you can check if it is valid.
https://en.wikipedia.org/wiki/Portable_Network_Graphics#File_format
I have made a little library that checks that the chunk layout is correct, and it checks that the crc code for each chunk is valid. Ready to consume as a npm package here:
https://www.npmjs.com/package/png-validator
Short answer is no.
As you note the browsers derive type from the file extension. Mac preview also seems to run off the extension. I'm assuming its because its faster reading the file name contained in the pointer, rather than looking up and reading the file on disk.
I made a copy of a jpg renamed with png.
I was able to consistently get the following from both images in chrome (should work in modern browsers).
ÿØÿà JFIFÿþ;CREATOR: gd-jpeg v1.0 (using IJG JPEG v62), quality = 90
Which you could hack out a String.indexOf('jpeg') check for image type.
Here is a fiddle to explore http://jsfiddle.net/bamboo/jkZ2v/1/
The ambigious line I forgot to comment in the example
console.log( /^(.*)$/m.exec(window.atob( image.src.split(',')[1] )) );
Splits the base64 encoded img data, leaving on the image
Base64 decodes the image
Matches only the first line of the image data
The fiddle code uses base64 decode which wont work in IE9, I did find a nice example using VB script that works in IE http://blog.nihilogic.dk/2008/08/imageinfo-reading-image-metadata-with.html
The code to load the image was taken from Joel Vardy, who is doing some cool image canvas resizing client side before uploading which may be of interest https://joelvardy.com/writing/javascript-image-upload
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.
With the new File API in Javascript you can read files in Javascript to create dataURLs to show clientside pictures clientside. I'm wondering if you can reach the File object within the FileReader's onload callback.
I will illustrate this with an example:
var div = document.createElement('div');
div.ondrop = function(e) {
e.preventDefault();
e.stopPropagation();
var files = e.dataTransfer.files;
for ( var i=0; i<files.length; i++ ) {
var file = files[i]; // this is the file I want!!
var filereader = new FileReader();
filereader.onload = function(e) {
this; // the FileReader object
e.target; // the same FileReader object
this.result; // the dataURL, something like data:image/jpeg;base64,.....
var img = document.createElement('img');
img.src = this.result;
img.title = file.fileName; // This won't be working
document.appendChild(img);
}
}
return false;
}
What I could do - what I do right now - is wrap the contents of the for loop in a function and execute it to create a new scope and keep a file in that scope like so:
for ( var i=0; i<files.length; i++ ) {
var _file = files[i]; // this is the file I want!!
(function(file) {
// do FileReader stuff here
})(_file);
}
I was just wondering... Maybe I'm missing something. Is there a way to get the File object from within the onload function of the FileReader? Both this and e.target are the FileReader object and not the File. Is there something in this or e that is the File?? I can't find it :(
Thanks a bunch.
PS. A fiddle: http://jsfiddle.net/rudiedirkx/ZWMRd/1/
I already found a way. Maybe not better than the scope wrapper, but I think it's neater:
for ( var i=0; i<files.length; i++ ) {
var file = files[i]; // this is the file I want!!
var filereader = new FileReader();
filereader.file = file;
filereader.onload = function(e) {
var file = this.file; // there it is!
// do stuff
}
}
There is now a much easier (apparently faster) way (sync!) to get a file's data URL:
img.src = URL.createObjectURL(file);
Demo on http://jsfiddle.net/rudiedirkx/ZWMRd/8/show/ of both methods, and the original problem illustrated (drag multiple images and check the title tooltips).
I don't think this.file is still supported. When I try to run the answer code, this.file is undefined whereas if I run the code from the question I get the expected results. I think you have to use the closure (at least this is how they do it on html5rocks (Example)).