I'm struggling to find documentation or examples of implementing an upload progress indicator using fetch.
This is the only reference I've found so far, which states:
Progress events are a high level feature that won't arrive in fetch for now. You can create your own by looking at the Content-Length header and using a pass-through stream to monitor the bytes received.
This means you can explicitly handle responses without a Content-Length differently. And of course, even if Content-Length is there it can be a lie. With streams you can handle these lies however you want.
How would I write "a pass-through stream to monitor the bytes" sent? If it makes any sort of difference, I'm trying to do this to power image uploads from the browser to Cloudinary.
NOTE: I am not interested in the Cloudinary JS library, as it depends on jQuery and my app does not. I'm only interested in the stream processing necessary to do this with native javascript and Github's fetch polyfill.
https://fetch.spec.whatwg.org/#fetch-api
Streams are starting to land in the web platform (https://jakearchibald.com/2016/streams-ftw/) but it's still early days.
Soon you'll be able to provide a stream as the body of a request, but the open question is whether the consumption of that stream relates to bytes uploaded.
Particular redirects can result in data being retransmitted to the new location, but streams cannot "restart". We can fix this by turning the body into a callback which can be called multiple times, but we need to be sure that exposing the number of redirects isn't a security leak, since it'd be the first time on the platform JS could detect that.
Some are questioning whether it even makes sense to link stream consumption to bytes uploaded.
Long story short: this isn't possible yet, but in future this will be handled either by streams, or some kind of higher-level callback passed into fetch().
My solution is to use axios, which supports this pretty well:
axios.request({
method: "post",
url: "/aaa",
data: myData,
onUploadProgress: (p) => {
console.log(p);
//this.setState({
//fileprogress: p.loaded / p.total
//})
}
}).then (data => {
//this.setState({
//fileprogress: 1.0,
//})
})
I have example for using this in react on github.
fetch: not possible yet
It sounds like upload progress will eventually be possible with fetch once it supports a ReadableStream as the body. This is currently not implemented, but it's in progress. I think the code will look something like this:
warning: this code does not work yet, still waiting on browsers to support it
async function main() {
const blob = new Blob([new Uint8Array(10 * 1024 * 1024)]); // any Blob, including a File
const progressBar = document.getElementById("progress");
const totalBytes = blob.size;
let bytesUploaded = 0;
const blobReader = blob.stream().getReader();
const progressTrackingStream = new ReadableStream({
async pull(controller) {
const result = await blobReader.read();
if (result.done) {
console.log("completed stream");
controller.close();
return;
}
controller.enqueue(result.value);
bytesUploaded += result.value.byteLength;
console.log("upload progress:", bytesUploaded / totalBytes);
progressBar.value = bytesUploaded / totalBytes;
},
});
const response = await fetch("https://httpbin.org/put", {
method: "PUT",
headers: {
"Content-Type": "application/octet-stream"
},
body: progressTrackingStream,
});
console.log("success:", response.ok);
}
main().catch(console.error);
upload: <progress id="progress" />
workaround: good ol' XMLHttpRequest
Instead of fetch(), it's possible to use XMLHttpRequest to track upload progress — the xhr.upload object emits a progress event.
async function main() {
const blob = new Blob([new Uint8Array(10 * 1024 * 1024)]); // any Blob, including a File
const uploadProgress = document.getElementById("upload-progress");
const downloadProgress = document.getElementById("download-progress");
const xhr = new XMLHttpRequest();
const success = await new Promise((resolve) => {
xhr.upload.addEventListener("progress", (event) => {
if (event.lengthComputable) {
console.log("upload progress:", event.loaded / event.total);
uploadProgress.value = event.loaded / event.total;
}
});
xhr.addEventListener("progress", (event) => {
if (event.lengthComputable) {
console.log("download progress:", event.loaded / event.total);
downloadProgress.value = event.loaded / event.total;
}
});
xhr.addEventListener("loadend", () => {
resolve(xhr.readyState === 4 && xhr.status === 200);
});
xhr.open("PUT", "https://httpbin.org/put", true);
xhr.setRequestHeader("Content-Type", "application/octet-stream");
xhr.send(blob);
});
console.log("success:", success);
}
main().catch(console.error);
upload: <progress id="upload-progress"></progress><br/>
download: <progress id="download-progress"></progress>
Update: as the accepted answer says it's impossible now. but the below code handled our problem for sometime. I should add that at least we had to switch to using a library that is based on XMLHttpRequest.
const response = await fetch(url);
const total = Number(response.headers.get('content-length'));
const reader = response.body.getReader();
let bytesReceived = 0;
while (true) {
const result = await reader.read();
if (result.done) {
console.log('Fetch complete');
break;
}
bytesReceived += result.value.length;
console.log('Received', bytesReceived, 'bytes of data so far');
}
thanks to this link: https://jakearchibald.com/2016/streams-ftw/
As already explained in the other answers, it is not possible with fetch, but with XHR. Here is my a-little-more-compact XHR solution:
const uploadFiles = (url, files, onProgress) =>
new Promise((resolve, reject) => {
const xhr = new XMLHttpRequest();
xhr.upload.addEventListener('progress', e => onProgress(e.loaded / e.total));
xhr.addEventListener('load', () => resolve({ status: xhr.status, body: xhr.responseText }));
xhr.addEventListener('error', () => reject(new Error('File upload failed')));
xhr.addEventListener('abort', () => reject(new Error('File upload aborted')));
xhr.open('POST', url, true);
const formData = new FormData();
Array.from(files).forEach((file, index) => formData.append(index.toString(), file));
xhr.send(formData);
});
Works with one or multiple files.
If you have a file input element like this:
<input type="file" multiple id="fileUpload" />
Call the function like this:
document.getElementById('fileUpload').addEventListener('change', async e => {
const onProgress = progress => console.log('Progress:', `${Math.round(progress * 100)}%`);
const response = await uploadFiles('/api/upload', e.currentTarget.files, onProgress);
if (response.status >= 400) {
throw new Error(`File upload failed - Status code: ${response.status}`);
}
console.log('Response:', response.body);
}
Also works with the e.dataTransfer.files you get from a drop event when building a file drop zone.
I don't think it's possible. The draft states:
it is currently lacking [in comparison to XHR] when it comes to request progression
(old answer):
The first example in the Fetch API chapter gives some insight on how to :
If you want to receive the body data progressively:
function consume(reader) {
var total = 0
return new Promise((resolve, reject) => {
function pump() {
reader.read().then(({done, value}) => {
if (done) {
resolve()
return
}
total += value.byteLength
log(`received ${value.byteLength} bytes (${total} bytes in total)`)
pump()
}).catch(reject)
}
pump()
})
}
fetch("/music/pk/altes-kamuffel.flac")
.then(res => consume(res.body.getReader()))
.then(() => log("consumed the entire body without keeping the whole thing in memory!"))
.catch(e => log("something went wrong: " + e))
Apart from their use of the Promise constructor antipattern, you can see that response.body is a Stream from which you can read byte by byte using a Reader, and you can fire an event or do whatever you like (e.g. log the progress) for every of them.
However, the Streams spec doesn't appear to be quite finished, and I have no idea whether this already works in any fetch implementation.
with fetch: now possible with Chrome >= 105 🎉
How to:
https://developer.chrome.com/articles/fetch-streaming-requests/
Currently not supported by other browsers (maybe that will be the case when you read this, please edit my answer accordingly)
Feature detection (source)
const supportsRequestStreams = (() => {
let duplexAccessed = false;
const hasContentType = new Request('', {
body: new ReadableStream(),
method: 'POST',
get duplex() {
duplexAccessed = true;
return 'half';
},
}).headers.has('Content-Type');
return duplexAccessed && !hasContentType;
})();
HTTP >= 2 required
The fetch will be rejected if the connection is HTTP/1.x.
Since none of the answers solve the problem.
Just for implementation sake, you can detect the upload speed with some small initial chunk of known size and the upload time can be calculated with content-length/upload-speed. You can use this time as estimation.
A possible workaround would be to utilize new Request() constructor then check Request.bodyUsed Boolean attribute
The bodyUsed attribute’s getter must return true if disturbed, and
false otherwise.
to determine if stream is distributed
An object implementing the Body mixin is said to be disturbed if
body is non-null and its stream is disturbed.
Return the fetch() Promise from within .then() chained to recursive .read() call of a ReadableStream when Request.bodyUsed is equal to true.
Note, the approach does not read the bytes of the Request.body as the bytes are streamed to the endpoint. Also, the upload could complete well before any response is returned in full to the browser.
const [input, progress, label] = [
document.querySelector("input")
, document.querySelector("progress")
, document.querySelector("label")
];
const url = "/path/to/server/";
input.onmousedown = () => {
label.innerHTML = "";
progress.value = "0"
};
input.onchange = (event) => {
const file = event.target.files[0];
const filename = file.name;
progress.max = file.size;
const request = new Request(url, {
method: "POST",
body: file,
cache: "no-store"
});
const upload = settings => fetch(settings);
const uploadProgress = new ReadableStream({
start(controller) {
console.log("starting upload, request.bodyUsed:", request.bodyUsed);
controller.enqueue(request.bodyUsed);
},
pull(controller) {
if (request.bodyUsed) {
controller.close();
}
controller.enqueue(request.bodyUsed);
console.log("pull, request.bodyUsed:", request.bodyUsed);
},
cancel(reason) {
console.log(reason);
}
});
const [fileUpload, reader] = [
upload(request)
.catch(e => {
reader.cancel();
throw e
})
, uploadProgress.getReader()
];
const processUploadRequest = ({value, done}) => {
if (value || done) {
console.log("upload complete, request.bodyUsed:", request.bodyUsed);
// set `progress.value` to `progress.max` here
// if not awaiting server response
// progress.value = progress.max;
return reader.closed.then(() => fileUpload);
}
console.log("upload progress:", value);
progress.value = +progress.value + 1;
return reader.read().then(result => processUploadRequest(result));
};
reader.read().then(({value, done}) => processUploadRequest({value,done}))
.then(response => response.text())
.then(text => {
console.log("response:", text);
progress.value = progress.max;
input.value = "";
})
.catch(err => console.log("upload error:", err));
}
I fished around for some time about this and just for everyone who may come across this issue too here is my solution:
const form = document.querySelector('form');
const status = document.querySelector('#status');
// When form get's submitted.
form.addEventListener('submit', async function (event) {
// cancel default behavior (form submit)
event.preventDefault();
// Inform user that the upload has began
status.innerText = 'Uploading..';
// Create FormData from form
const formData = new FormData(form);
// Open request to origin
const request = await fetch('https://httpbin.org/post', { method: 'POST', body: formData });
// Get amount of bytes we're about to transmit
const bytesToUpload = request.headers.get('content-length');
// Create a reader from the request body
const reader = request.body.getReader();
// Cache how much data we already send
let bytesUploaded = 0;
// Get first chunk of the request reader
let chunk = await reader.read();
// While we have more chunks to go
while (!chunk.done) {
// Increase amount of bytes transmitted.
bytesUploaded += chunk.value.length;
// Inform user how far we are
status.innerText = 'Uploading (' + (bytesUploaded / bytesToUpload * 100).toFixed(2) + ')...';
// Read next chunk
chunk = await reader.read();
}
});
const req = await fetch('./foo.json');
const total = Number(req.headers.get('content-length'));
let loaded = 0;
for await(const {length} of req.body.getReader()) {
loaded = += length;
const progress = ((loaded / total) * 100).toFixed(2); // toFixed(2) means two digits after floating point
console.log(`${progress}%`); // or yourDiv.textContent = `${progress}%`;
}
Key part is ReadableStream ≪obj_response.body≫.
Sample:
let parse=_/*result*/=>{
console.log(_)
//...
return /*cont?*/_.value?true:false
}
fetch('').
then(_=>( a/*!*/=_.body.getReader(), b/*!*/=z=>a.read().then(parse).then(_=>(_?b:z=>z)()), b() ))
You can test running it on a huge page eg https://html.spec.whatwg.org/ and https://html.spec.whatwg.org/print.pdf . CtrlShiftJ and load the code in.
(Tested on Chrome.)
I have a project that has functions that read files and extract their hash code. After these hash codes are extracted in the project, subfiles are built one by one. Finally, what I want to do is to throw all these hash codes into an array and create a json file. I need to do this after the IterateFolders() function has run and finished in readDirectory function. But console.log is running on a bottom line without waiting for this function, please help.
My functions are as follows:
//Calculate build time
function getBuildTime(start,end) {
let time = (end - start);
let buildTime = `${new Date().toLocaleDateString()} ${new Date().toLocaleTimeString()} Build time: ${time} ms \n`
fs.writeFile('build-time.log', buildTime,function (err) { //output log file
if (err) return console.log(err);
});
}
//async metaHash calculation from folder path
async function computeMetaHash(folder, inputHash = null) {
const hash = inputHash ? inputHash : createHash('sha256');
const info = await fsp.readdir(folder, { withFileTypes: true });
//construct a string from the modification date, the filename and the filesize
for (let item of info) {
const fullPath = path.join(folder, item.name)
if (item.isFile()) {
const statInfo = await fsp.stat(fullPath); //stat return all informations about file
// compute hash string name:size:mtime
const fileInfo = `${fullPath}:${statInfo.size}:${statInfo.mtimeMs}`;
hash.update(fileInfo);
} else if (item.isDirectory()) {
// recursively walk sub-folders
await computeMetaHash(fullPath, hash);
}
}
// if not being called recursively, get the digest and return it as the hash result
if (!inputHash) {
return hash.digest('base64');
}
}
async function iterateFolders(folderPath) {
folderPath.forEach(function (files) {
//function takes folder path as inputh
computeMetaHash(files).then(result => { //call create hash function
console.log({"path":files,"hashCode":result});
}).then(()=>{ //build fragments
//The files is array, so each. files is the folder name. can handle the folder.
console.log("%s build...", files);
execSync(`cd ${files} && npm run build`, { encoding: 'utf-8' });
}).then(()=>{// Finish timing
end = new Date().getTime();
getBuildTime(start,end);
}).catch(err => {
console.log(err);
});
});
}
async function readDirectory() {
let files = await readdir(p)
const folderPath = files.map(function (file) {
//return file or folder path
return path.join(p, file);
}).filter(function (file) {
//use sync judge method. The file will add next files array if the file is directory, or not.
return fs.statSync(file).isDirectory();
})
//check hash.json exist or not
if (fs.existsSync(hashFile)) {
// path exists
console.log("File exists: ", hashFile);
}
else
{
//This is the first pipeline, all fragments will build then hash.json will created.
console.log(hashFile," does NOT exist, build will start and hash.json will created:");
// Start timing
start = new Date().getTime();
iterateFolders(folderPath,files);
console.log("IT WILL BE LAST ONE ")
}
}
readDirectory();
Well if you want to wait for its execution, then you have to use await :) Currently it's just iterateFolders(folderPath,files);, so you run it, but you don't wait for it.
await iterateFolders(folderPath,files);
That's your first issue. Then this method runs some loop and calls some other methods. But first async-await needs to return a promise (which you do not do). And second - it doesn't work in forEach, as stated in the comments above. Read Using async/await with a forEach loop for more details.
Fix those three issues and you'll make it.
In the iterateFolders function, you need to await computeMetaHash calls. To do so you can either use a for loop instead of calling forEach on folderPath or change forEach to map and use Promise.all.
Using the for loop method (synchronous):
async function iterateFolders(folderPath) {
for (let files of folderPath) {
//function takes folder path as inputh
await computeMetaHash(files).then(result => { //call create hash function
console.log({"path":files,"hashCode":result});
}).then(()=>{ //build fragments
//The files is array, so each. files is the folder name. can handle the folder.
console.log("%s build...", files);
execSync(`cd ${files} && npm run build`, { encoding: 'utf-8' });
}).then(()=>{// Finish timing
end = new Date().getTime();
getBuildTime(start,end);
}).catch(err => {
console.log(err);
});
}
}
Using the Promise.all method (asynchronous):
async function iterateFolders(folderPath) {
return Promise.all(folderPath.map(function (files) {
//function takes folder path as inputh
return computeMetaHash(files).then(result => { //call create hash function
console.log({"path":files,"hashCode":result});
}).then(()=>{ //build fragments
//The files is array, so each. files is the folder name. can handle the folder.
console.log("%s build...", files);
execSync(`cd ${files} && npm run build`, { encoding: 'utf-8' });
}).then(()=>{// Finish timing
end = new Date().getTime();
getBuildTime(start,end);
}).catch(err => {
console.log(err);
});
}));
}
If you prefer, using async/await also allows you to get rid of the then and catch in both methods which I believe makes it a little easier to read and understand.
Here's an example using the Promise.all method:
async function iterateFolders(folderPath) {
return Promise.all(folderPath.map(async (files) => {
try {
const result = await computeMetaHash(files);
console.log({ path: files, hashCode: result });
// build fragments
//The files is array, so each. files is the folder name. can handle the folder.
console.log('%s build...', files);
execSync(`cd ${files} && npm run build`, { encoding: 'utf-8' });
// Finish timing
const end = Date.now();
getBuildTime(start, end);
} catch(err) {
console.log(err);
}
}));
}
You might also want to check out for await... of
Note: you also need to await iterateFolders when it's called in readDirectory.
I need to download large no of files(say 100k, each file size 0.2 - 1 MB) from aws s3 to node js server. The code I am using is
app.get('/api/download-all', function(req, res) {
res.json({status: 'download initiated'})
downloadFromS3(getDocs());
});
The function that downloads the audios is
function downloadFromS3(docs){
docs.forEach((doc, fileIndex)=>{
var s3FilePath = doc.wav
var fileName = s3FilePath.split('/').pop();
var s3Params = {Bucket: 'zzzzz', Key: s3FilePath};
var file = fs.createWriteStream(dir + '/' + fileName);
console.log(downloadSession);
s3.getObject(s3Params)
.on('httpData', function (chunk) {
console.log("file writing happening", fileName);
file.write(chunk);
})
.send();
}); }
Here the download function fires S3.getObject call as many times as the no of files to download. it doesn't wait for the status of the file. its almost like some 100k (in my case) s3.getObject has been made before letting a file to download. is this a right way or should I wait for one file to download and invoke the s3 call after that. what will be the right approach.
2) There is one other issue I am facing with this code. Once I make the download api call from UI the server gets busy with download. its not returning any requests from the UI. all requests gets pending. Is there is anyway to do the download in background. I had gone through some approaches like fork a child process or a web worker to handle this. I am not sure which one to use. what is the best way to handle this.
I'd advise an in-between approach. Kicking off 100k downloads in parallel is really not a good idea. But similarly, waiting for each download to fully complete won't utilise your full bandwidth. I'd suggest a solution that "pools" jobs - e.g., you create a pool of promises, each of which can download one file at a time, as soon as it finishes it starts the next.
I've been using a function like this:
Promise.pool = function pool(funcs, inParallel, progressCallback) {
const promises = [];
const results = [];
function getNext() {
if (funcs.length) {
return funcs.pop()()
.catch(() => {})
.then((res) => {
results.push(res);
if (progressCallback) {
progressCallback(results);
}
return getNext();
});
}
}
for (let i = 0; i < Math.min(inParallel, funcs.length); i++) {
promises.push(getNext());
}
return Promise.all(promises)
.then(() => results);
};
Then you'd define an array of functions, each downloads one file and returns a promise which resolves on completion:
const funcs = docs.map((doc) => {
return () => {
return new Promise((resolve) => {
var s3FilePath = doc.wav
var fileName = s3FilePath.split('/').pop();
var s3Params = {Bucket: 'zzzzz', Key: s3FilePath};
var file = fs.createWriteStream(dir + '/' + fileName);
console.log(downloadSession);
s3.getObject(s3Params)
.on('httpData', function (chunk) {
console.log("file writing happening", fileName);
file.write(chunk);
})
.on("end", () => resolve())
.send();
});
}
});
Finally, you'd use it like this:
const inParallel = 32;
function callback(partialResults) {
//console log, whatever
}
Promise.pool(funcs, inParallel, callback)
.then(() => console.log("all done!"));
I am working on MEAN stack application and I am using AWS SDK to upload multiple files to S3. I am using busboy and AWS SDK.
Code:
var inputObj = {};
var busboy = new Busboy({ headers: req.headers });
// The file upload has completed
busboy.on('finish', function() {
console.log('Upload finished.....');
var file = [];
const file1 = req.files.clogo;
const file2 = req.files.cbanner1;
const file3 = req.files.cbanner2;
const file4 = req.files.cbanner3;
const file5 = req.files.cbanner4;
const file6 = req.files.clongHeader;
file.push(file1);
file.push(file2);
file.push(file3);
file.push(file4);
file.push(file5);
file.push(file6);
multipleUploadToS3(req.body.cname, file, function(fileName) {
console.log("client file upload finished.....");
if(fileName.length == 6){
inputObj.clogo = fileName[0];
inputObj.cbanner1 = fileName[1];
inputObj.cbanner2 = fileName[2];
inputObj.cbanner3 = fileName[3];
inputObj.cbanner4 = fileName[4];
inputObj.clongHeader = fileName[5];
console.log(inputObj);
var clientObj = new client(inputObj);
clientObj.save(function(err, client) {
console.log("Client Saved.....");
if (err) {
return res.status(400).send({
message: errorHandler.getErrorMessage(err)
});
} else {
res.json(client);
}
});
}
});
});
req.pipe(busboy);
File Upload Method:
function multipleUploadToS3(client, file, callback) {
console.log("multipleUpload to S3");
console.log(client);
console.log(file);
let s3bucket = new AWS.S3({
accessKeyId: IAM_USER_KEY,
secretAccessKey: IAM_USER_SECRET,
Bucket: BUCKET_NAME,
});
var fileNames = [];
for(var i=0; i<file.length; i++){
s3bucket.createBucket(function () {
var params = {
Bucket: BUCKET_NAME,
Key: client+ '/' + file[i].name,
Body: file[i].data,
};
s3bucket.upload(params, function (err, data) {
if (err) {
console.log('error in callback');
console.log(err);
}
console.log('success');
//console.log(data.key);
fileNames.push(data.key);
if(i == file.length){ callback(fileNames);}
});
});
}
};
The issue: file upload is asynchronous so for example if file1 I am uploading is honest.jpg then I want multipleUploadToS3 method to return file name after its done uploading to S3. I am binding this in inputObj keys which will be saved to mongo db. so inputObj.logo should have logo.png in it not the banner image which is happening due to asynchronous call.
This is working for a single file but failing for multiple files.
The problem is because for loop is synchronous and file upload is asynchronous.
Take a look at this example below,
for(var i = 0; i<5;i++) {
setTimeout(function(){ console.log(i); }, 100);
}
The above loop will print 5 for 5 times i.e 55555.
This behaviour is because for loop gets executed immediately making i=5 and when timeout gets executed it prints "i" value 5 for 5 times. 5 times because setTimeout is pushed in the queue for five times.
There are two ways to solve the problem you are facing
You can use Recursion.
Use neo-async(async-parallel) lib to control the async flow of javascript(Nodejs). click here for neo-async lib
Hope this clears your doubt. Please comment for more info.
I am getting confuse how to read a list of files recursively.
Assume I have 3 text files in my filesytem api root directory
text1.txt
text2.txt
text3.txt
My goal is to read each text files one by one and then concatenate all the entries in each file into one string but I am currently at lost
how to do this in Javascript FileSystem API.
window.requestFileSystem(window.TEMPORARY, 1024*1024, onInitFs, errorHandler);
function onInitFs(fs) {
var dirReader = fs.root.createReader();
var entries = [];
// Call the reader.readEntries() until no more results are returned.
var readEntries = function() {
dirReader.readEntries (function(results) {
if (!results.length) {
readAllFiles(results);
} else {
entries = entries.concat(toArray(results));
readEntries();
}
}, errorHandler);
};
readEntries(); // Start reading dirs.
}
function readAllFiles(entries){
//Loop thru all the files and read each entries
}
I have seen how to read one text file but I dont know how to implement the reading of all files and concatenate the value.
They all implement callback functions so I am getting confused on how to handle it. Any points please?
I actually have been basing all my works in this http://www.html5rocks.com/en/tutorials/file/filesystem
UPDATE 2
As per #Johan
I actually changed my code to make use of callback
window.requestFileSystem(window.TEMPORARY, 1024*1024, onInitFs, errorHandler);
function onInitFs(fs) {
var dirReader = fs.root.createReader();
var entries = [];
// Call the reader.readEntries() until no more results are returned.
var readEntries = function() {
dirReader.readEntries (function(results) {
if (!results.length) {
readAllFiles(results, concatMessages);
} else {
entries = entries.concat(toArray(results));
readEntries();
}
}, errorHandler);
};
readEntries(); // Start reading dirs.
}
var concatMessage = '';
function concatMessages(message){
concatMessage += message;
}
function readAllFiles(logs, callBack) {
logs.forEach(function(entry, iCtr) {
var message;
entry.file(function(file) {
var reader = new FileReader();
reader.onloadend = function(e) {
//message += this.result;
if(callBack)
callBack('==================' + iCtr + '==========================');
callBack(this.result);
};
reader.readAsText(file); // Read the file as plaintext.
}, function(err) {
console.log(err);
});
});
}
My only problem is this, the callback function is not sequential.
It reads text2.txt first then text3.txt then text1.txt so the end result is not sequential which is not what I want to do. Any more hints?
Highly recommend you consider using something like caolan's async library to accomplish this.
You can do something like this:
async.each(openFiles, function(file, callback) {
// Perform operation on file here.
console.log('Processing file ' + file);
callback();
}, function(err) {
// if any of the file processing produced an error, err would equal that error
if (err) {
// One of the iterations produced an error.
// All processing will now stop.
console.log('A file failed to process');
} else {
// do your concatenation here
}
});