How to read file content in a javascript variable?

How to read file content in a javascript variable? - javascript

I got a small script to split the text inside 'var foo' after every 4 characters. It is working fine.
but my actual data is in a text file say 'a.txt'. How do I take this entire file text in 'var foo'. and write the split output to another text file?
var foo = "this is sample text !!!";
var arr = [];
for (var i = 0; i < foo.length; i++) {
if (i % 4 == 0 && i != 0)
arr.push(foo.substring(i - 4, i));
if (i == foo.length - 1)
arr.push(foo.substring(i - (i % 4), i+1));
}
document.write(arr);
console.log(arr);

To get the content of the file you need to select a file using an input tag.
<!DOCTYPE html>
<head>
<meta charset="UTF-8">
</head>
<body>
<input id="input" type="file" accept="text/plain">
<script src="script.js"></script>
</body>
A good moment to read the content of the file is in the change event.
const input = document.querySelector("#input");
input.addEventListener("change", () => {
const file = input.files.item(0);
});
To read the content of the file as a string you need to convert it.
function fileToText(file, callback) {
const reader = new FileReader();
reader.readAsText(file);
reader.onload = () => {
callback(reader.result);
};
}
The content of the file as a string will be available to the the callback function. You can create a link and use the click event to download the string into a text file.
function save(content, fileName, mime) {
const blob = new Blob([content], {
tipe: mime
});
const url = URL.createObjectURL(blob);
const a = document.createElement("a");
a.href = url;
a.download = fileName;
a.click();
}
Here is the complete code
const input = document.querySelector("#input");
input.addEventListener("change", () => {
const file = input.files.item(0);
fileToText(file, (text) => {
save(text, "fileName.txt", "text/plain");
});
});
function fileToText(file, callback) {
const reader = new FileReader();
reader.readAsText(file);
reader.onload = () => {
callback(reader.result);
};
}
function save(content, fileName, mime) {
const blob = new Blob([content], {
tipe: mime
});
const url = URL.createObjectURL(blob);
const a = document.createElement("a");
a.href = url;
a.download = fileName;
a.click();
}
<!DOCTYPE html>
<head>
<meta charset="UTF-8">
</head>
<body>
<input id="input" type="file" accept="text/plain">
<script src="script.js"></script>
</body>
You can read more about manipulating files in JavaScript here: https://www.html5rocks.com/en/tutorials/file/dndfiles/

Solution to this helped me :
How do I load the contents of a text file into a javascript variable?
var client = new XMLHttpRequest();
client.open('GET', '/foo.txt');
client.onreadystatechange = function() {
alert(client.responseText);
}
client.send();

Related

how should I go by making a audio file converter in react

I am trying to make an audio file converter that lets a user submit a file. Then uses JavaScripts Web Audio API to convert the pitch and stretch the file. I have gotten as far as uploading the file, use file reader to onload a function that stretches and converts the pitch. Now I am trying to export that file with the changes and I can right now only download the original file but not with the changes. I dont know how to assign file = buffer because it's from another class. How should I got by making this happen?
convertFile () {
var fileInput = document.getElementById('audio-file')
var ctx = new AudioContext()
var convertFiles = document.getElementById('convert_button')
//load audio file listener
convertFiles.addEventListener("click", function() {
if (fileInput.files[0] == undefined) {
console.log("no file found")
return false
}
var reader1 = new FileReader()
reader1.onload = function(ev) {
ctx.decodeAudioData(ev.target.result). then(function(buffer){
var soundSource = ctx.createBufferSource()
soundSource.buffer = buffer
// create the stretch
soundSource.playbackRate.linearRampToValueAtTime(0.0185, ctx.currentTime)
//connect source
soundSource.connect(ctx.destination)
// convert pitch
var pitchChange = ctx.createBiquadFilter()
pitchChange.type = 'highpass'
pitchChange.frequency.value = 432
pitchChange.connect(ctx.destination)
})
}
reader1.readAsArrayBuffer(fileInput.files[0])
})
let file = fileInput.files[0]
let url = URL.createObjectURL(file)
let link = document.createElement('a')
link.href = url
link.download = file.name
link.click()
link = null
URL.revokeObjectURL(url)
}
render() {
return (
<div className="sec2">
<input type="file" id="audio-file" accept="audio/mpeg, audio/ogg, audio/*" name="file" onChange={this.uploadFile} />
<button type="button" id="convert_button" onClick={this.convertFile}>Convert to 432Hz</button>
<download onClick={this.downloadFile}>Download File</download>
</div>
)
}
}
export default ConverterSec2

I started looking into this... I fixed a couple issues such as the audio file being loaded twice. However this is work in progress answer... I haven't figure out the saving part yet.
class ConverterSec2 extends React.Component {
uploadFile = ({ target: { files } }) => {
console.log(files[0])
let data = new FormData()
data.append('file', files[0])
}
convertFile () {
var fileInput = document.getElementById('audio-file')
var ctx = new AudioContext()
var convertFiles = document.getElementById('convert_button')
//load audio file listener
if (fileInput.files[0] == undefined) {
console.log("no file found")
return false
}
var soundSource = ctx.createBufferSource();
var reader1 = new FileReader()
reader1.onload = function(ev) {
ctx.decodeAudioData(ev.target.result).then(function(buffer){
soundSource.buffer = buffer
// create the stretch
soundSource.playbackRate.linearRampToValueAtTime(0.0185, ctx.currentTime)
//connect source
soundSource.connect(ctx.destination)
// convert pitch
var pitchChange = ctx.createBiquadFilter()
pitchChange.type = 'highpass'
pitchChange.frequency.value = 432
pitchChange.connect(ctx.destination)
})
}
reader1.readAsArrayBuffer(fileInput.files[0]);
}
downloadFile() {
let fileInput = document.getElementById('audio-file')
let file = fileInput.files[0]
let url = URL.createObjectURL(file)
let link = document.createElement('a')
link.href = url
link.download = file.name
link.click()
link = null
URL.revokeObjectURL(url)
}
render() {
return (
<div className="sec2">
<input type="file" id="audio-file" accept="audio/mpeg, audio/ogg, audio/*" name="file" onChange={this.uploadFile} />
<button type="button" id="convert_button" onClick={this.convertFile}>Convert to 432Hz</button>
<button onClick={this.downloadFile}>Download File</button>
</div>
)
}
}
Live Demo

Client side Javascript get video width/height before upload

I've been trying to piece together a combination of HTML5 video tag + the FileReader API but I haven't figured out how to get the dimensions of a video that a user is providing from their own computer.
Here is what I am referencing for width/ height:
HTML5 Video Dimensions
<video id="foo" src="foo.mp4"></video>
var vid = document.getElementById("foo");
vid.videoHeight; // returns the intrinsic height of the video
vid.videoWidth; // returns the intrinsic width of the video
But I want to know if it's possible to do this with a file from a user's computer (that they have selected via a normal input html tag).
Thanks!

A bit unclean solution using basic FileReader + Data URL.
<html>
<head>
<style>
div {
margin: 20px;
}
</style>
</head>
<body>
<h1>Get Dimensions</h1>
<div>
<label for="load-file">Load a file:</label>
<input type="file" id="load-file">
</div>
<div>
<button type="button" id="done-button">Get me dimensions</button>
</div>
<script src="//cdn.jsdelivr.net/jquery/2.1.4/jquery.js"></script>
<script>
(function ($) {
$('#done-button').on('click', function () {
var file = $('#load-file')[0].files[0];
var reader = new FileReader();
var fileType = file.type;
console.log("type", fileType);
reader.addEventListener("load", function () {
var dataUrl = reader.result;
var videoId = "videoMain";
var $videoEl = $('<video id="' + videoId + '"></video>');
$("body").append($videoEl);
$videoEl.attr('src', dataUrl);
var videoTagRef = $videoEl[0];
videoTagRef.addEventListener('loadedmetadata', function(e){
console.log(videoTagRef.videoWidth, videoTagRef.videoHeight);
});
}, false);
if (file) {
reader.readAsDataURL(file);
}
});
})(jQuery);
</script>
</body>
</html>

Here is a simple and fast solution to get a video's size before upload.
It doesn't require any dependency.
const url = URL.createObjectURL(file);
const $video = document.createElement("video");
$video.src = url;
$video.addEventListener("loadedmetadata", function () {
console.log("width:", this.videoWidth);
console.log("height:", this.videoHeight);
});

const onSelectVideo = (files) => {
const file = files[0];
const url = URL.createObjectURL(file);
let videoId = "videoMain";
const video = document.createElement("video");
const body = document.getElementsByTagName("body");
video.setAttribute("src", url);
video.setAttribute("videoId", videoId);
body[0]?.append(video);
let videoTagRef = document.querySelector("[videoId='videoMain']");
videoTagRef.addEventListener("loadedmetadata", function (e) {
console.log(videoTagRef.videoWidth, videoTagRef.videoHeight);
});}

Force browser to download image files on click

I need the browser to download the image files just as it does while clicking on an Excel sheet.
Is there a way to do this using client-side programming only?
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<script type="text/javascript" src="Scripts/jquery-1.10.2.js">
$(document).ready(function () {
$("*").click(function () {
$("p").hide();
});
});
</script>
</head>
<script type="text/javascript">
document.onclick = function (e) {
e = e || window.event;
var element = e.target || e.srcElement;
if (element.innerHTML == "Image") {
//someFunction(element.href);
var name = element.nameProp;
var address = element.href;
saveImageAs1(element.nameProp, element.href);
return false; // Prevent default action and stop event propagation
}
else
return true;
};
function saveImageAs1(name, adress) {
if (confirm('you wanna save this image?')) {
window.win = open(adress);
//response.redirect("~/testpage.html");
setTimeout('win.document.execCommand("SaveAs")', 100);
setTimeout('win.close()', 500);
}
}
</script>
<body>
<form id="form1" runat="server">
<div>
<p>
Excel<br />
Image
</p>
</div>
</form>
</body>
</html>
How should it work in case of downloading an Excel sheet (what browsers do)?

Using HTML5 you can add the attribute 'download' to your links.
<a href="/path/to/image.png" download>
Compliant browsers will then prompt to download the image with the same file name (in this example image.png).
If you specify a value for this attribute, then that will become the new filename:
<a href="/path/to/image.png" download="AwesomeImage.png">
UPDATE: As of spring 2018 this is no longer possible for cross-origin hrefs. So if you want to create <a href="https://i.imgur.com/IskAzqA.jpg" download> on a domain other than imgur.com it will not work as intended. Chrome deprecations and removals announcement

I managed to get this working in Chrome and Firefox too by appending a link to the to document.
var link = document.createElement('a');
link.href = 'images.jpg';
link.download = 'Download.jpg';
document.body.appendChild(link);
link.click();
document.body.removeChild(link);

Leeroy & Richard Parnaby-King:
UPDATE: As of spring 2018 this is no longer possible for cross-origin
hrefs. So if you want to create on a domain other than imgur.com it
will not work as intended. Chrome deprecations and removals
announcement
function forceDownload(url, fileName){
var xhr = new XMLHttpRequest();
xhr.open("GET", url, true);
xhr.responseType = "blob";
xhr.onload = function(){
var urlCreator = window.URL || window.webkitURL;
var imageUrl = urlCreator.createObjectURL(this.response);
var tag = document.createElement('a');
tag.href = imageUrl;
tag.download = fileName;
document.body.appendChild(tag);
tag.click();
document.body.removeChild(tag);
}
xhr.send();
}

A more modern approach using Promise and async/await :
async function toDataURL(url) {
const blob = await fetch(url).then(res => res.blob());
return URL.createObjectURL(blob);
}
then
async function download() {
const a = document.createElement("a");
a.href = await toDataURL("https://cdn1.iconfinder.com/data/icons/ninja-things-1/1772/ninja-simple-512.png");
a.download = "myImage.png";
document.body.appendChild(a);
a.click();
document.body.removeChild(a);
}
Find documentation here: https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch

Update Spring 2018
<a href="/path/to/image.jpg" download="FileName.jpg">
While this is still supported, as of February 2018 chrome disabled this feature for cross-origin downloading meaning this will only work if the file is located on the same domain name.
I figured out a workaround for downloading cross domain images after Chrome's new update which disabled cross domain downloading. You could modify this into a function to suit your needs. You might be able to get the image mime-type (jpeg,png,gif,etc) with some more research if you needed to. There may be a way to do something similar to this with videos as well. Hope this helps someone!
Leeroy & Richard Parnaby-King:
UPDATE: As of spring 2018 this is no longer possible for cross-origin
hrefs. So if you want to create on a domain other
than imgur.com it will not work as intended. Chrome deprecations and
removals announcement
var image = new Image();
image.crossOrigin = "anonymous";
image.src = "https://is3-ssl.mzstatic.com/image/thumb/Music62/v4/4b/f6/a2/4bf6a267-5a59-be4f-6947-d803849c6a7d/source/200x200bb.jpg";
// get file name - you might need to modify this if your image url doesn't contain a file extension otherwise you can set the file name manually
var fileName = image.src.split(/(\\|\/)/g).pop();
image.onload = function () {
var canvas = document.createElement('canvas');
canvas.width = this.naturalWidth; // or 'width' if you want a special/scaled size
canvas.height = this.naturalHeight; // or 'height' if you want a special/scaled size
canvas.getContext('2d').drawImage(this, 0, 0);
var blob;
// ... get as Data URI
if (image.src.indexOf(".jpg") > -1) {
blob = canvas.toDataURL("image/jpeg");
} else if (image.src.indexOf(".png") > -1) {
blob = canvas.toDataURL("image/png");
} else if (image.src.indexOf(".gif") > -1) {
blob = canvas.toDataURL("image/gif");
} else {
blob = canvas.toDataURL("image/png");
}
$("body").html("<b>Click image to download.</b><br><a download='" + fileName + "' href='" + blob + "'><img src='" + blob + "'/></a>");
};
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

var pom = document.createElement('a');
pom.setAttribute('href', 'data:application/octet-stream,' + encodeURIComponent(text));
pom.setAttribute('download', filename);
pom.style.display = 'none';
document.body.appendChild(pom);
pom.click();
document.body.removeChild(pom);

This is a general solution to your problem. But there is one very important part that the file extension should match your encoding. And of course, that content parameter of downlowadImage function should be base64 encoded string of your image.
const clearUrl = url => url.replace(/^data:image\/\w+;base64,/, '');
const downloadImage = (name, content, type) => {
var link = document.createElement('a');
link.style = 'position: fixed; left -10000px;';
link.href = `data:application/octet-stream;base64,${encodeURIComponent(content)}`;
link.download = /\.\w+/.test(name) ? name : `${name}.${type}`;
document.body.appendChild(link);
link.click();
document.body.removeChild(link);
}
['png', 'jpg', 'gif'].forEach(type => {
var download = document.querySelector(`#${type}`);
download.addEventListener('click', function() {
var img = document.querySelector('#img');
downloadImage('myImage', clearUrl(img.src), type);
});
});
a gif image: <image id="img" src="data:image/gif;base64,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" />
<button id="png">Download PNG</button>
<button id="jpg">Download JPG</button>
<button id="gif">Download GIF</button>

Create a function that recibe the image url and file name and call the funcion using a button.
function downloadImage(url, name){
fetch(url)
.then(resp => resp.blob())
.then(blob => {
const url = window.URL.createObjectURL(blob);
const a = document.createElement('a');
a.style.display = 'none';
a.href = url;
// the filename you want
a.download = name;
document.body.appendChild(a);
a.click();
window.URL.revokeObjectURL(url);
})
.catch(() => alert('An error sorry'));
}
<button onclick="downloadImage('https://upload.wikimedia.org/wikipedia/commons/thumb/0/02/Stack_Overflow_logo.svg/1280px-Stack_Overflow_logo.svg.png', 'LogoStackOverflow.png')" >DOWNLOAD</button>
Codepen.io Force image download with JavaScript
vladi.codes

You can directly download this file using anchor tag without much code.Copy the snippet and paste in your text-editor and try it...!
<html>
<head>
</head>
<body>
<div>
<img src="https://upload.wikimedia.org/wikipedia/commons/1/1f/SMirC-thumbsup.svg" width="200" height="200">
Download Image
</div>
</body>
</html>

In 2020 I use Blob to make local copy of image, which browser will download as a file. You can test it on this site.
(function(global) {
const next = () => document.querySelector('.search-pagination__button-text').click();
const uuid = () => Math.random().toString(36).substring(7);
const toBlob = (src) => new Promise((res) => {
const img = document.createElement('img');
const c = document.createElement("canvas");
const ctx = c.getContext("2d");
img.onload = ({target}) => {
c.width = target.naturalWidth;
c.height = target.naturalHeight;
ctx.drawImage(target, 0, 0);
c.toBlob((b) => res(b), "image/jpeg", 0.75);
};
img.crossOrigin = "";
img.src = src;
});
const save = (blob, name = 'image.png') => {
const a = document.createElement("a");
a.href = URL.createObjectURL(blob);
a.target = '_blank';
a.download = name;
a.click();
};
global.download = () => document.querySelectorAll('.search-content__gallery-results figure > img[src]').forEach(async ({src}) => save(await toBlob(src), `${uuid()}.png`));
global.next = () => next();
})(window);

Try this:
<a class="button" href="http://www.glamquotes.com/wp-content/uploads/2011/11/smile.jpg" download="smile.jpg">Download image</a>

You can do
const urls = ['image.png', 'image1.png'];
urls.forEach((url) => {
window.open(url, "_blank");
});

// Pass desired URL as a param
function saveAs(uri) {
fetch(uri)
.then(res => res.blob()) // Gets the response and returns it as a blob
.then(blob => {
// Here, I use it to make an image appear on the page
let objectURL = URL.createObjectURL(blob);
let myImage = new Image();
myImage.href = blob;
myImage.download = generateFileName();
//Firefox requires the link to be in the body
document.body.appendChild(myImage);
//simulate click
myImage.click();
//remove the link when done
document.body.removeChild(myImage);
});
}
// Generate filenames for the image which is to be downloaded
function generateFileName() {
return `img${Math.floor(Math.random() * 90000) + 10000}`;
}

<html>
<head>
<script type="text/javascript">
function prepHref(linkElement) {
var myDiv = document.getElementById('Div_contain_image');
var myImage = myDiv.children[0];
linkElement.href = myImage.src;
}
</script>
</head>
<body>
<div id="Div_contain_image"><img src="YourImage.jpg" alt='MyImage'></div>
<a href="#" onclick="prepHref(this)" download>Click here to download image</a>
</body>
</html>

<!DOCTYPE html>
<html>
<body>
<button onclick="forceDownload('http://localhost:4000/1-2-free-png-image.png','test.png')">Download</button>
<script>
function forceDownload(url, fileName){
var xhr = new XMLHttpRequest();
xhr.open("GET", url, true);
xhr.responseType = "blob";
xhr.onload = function(){
var urlCreator = window.URL || window.webkitURL;
var imageUrl = urlCreator.createObjectURL(this.response);
var tag = document.createElement('a');
tag.href = imageUrl;
tag.download = fileName;
document.body.appendChild(tag);
tag.click();
document.body.removeChild(tag);
}
xhr.send();
}
</script>
</body>
</html>

I found that
<a href="link/to/My_Image_File.jpeg" download>Download Image File</a>
did not work for me. I'm not sure why.
I have found that you can include a ?download=true parameter at the end of your link to force a download. I think I noticed this technique being used by Google Drive.
In your link, include ?download=true at the end of your href.
You can also use this technique to set the filename at the same time.
In your link, include ?download=true&filename=My_Image_File.jpeg at the end of your href.

What about using the .click() function and the tag?
(Compressed version)
<a id="downloadtag" href="examplefolder/testfile.txt" hidden download></a>
<button onclick="document.getElementById('downloadtag').click()">Download</button>
Now you can trigger it with js. It also doesn't open, as other examples, image and text files!
(js-function version)
function download(){
document.getElementById('downloadtag').click();
}
<!-- HTML -->
<button onclick="download()">Download</button>
<a id="downloadtag" href="coolimages/awsome.png" hidden download></a>

You don't need to write js to do that, simply use:
Download image
And the browser itself will automatically download the image.
If for some reason it doesn't work add the download attribute.
With this attribute you can set a name for the downloadable file:
Download image

How to read text file in JavaScript

I am trying to load a text file into my JavaScript file and then read the lines from that file in order to get information, and I tried the FileReader but it does not seem to be working. Can anyone help?
function analyze(){
var f = new FileReader();
f.onloadend = function(){
console.log("success");
}
f.readAsText("cities.txt");
}

Yeah it is possible with FileReader, I have already done an example of this, here's the code:
<!DOCTYPE html>
<html>
<head>
<title>Read File (via User Input selection)</title>
<script type="text/javascript">
var reader; //GLOBAL File Reader object for demo purpose only
/**
* Check for the various File API support.
*/
function checkFileAPI() {
if (window.File && window.FileReader && window.FileList && window.Blob) {
reader = new FileReader();
return true;
} else {
alert('The File APIs are not fully supported by your browser. Fallback required.');
return false;
}
}
/**
* read text input
*/
function readText(filePath) {
var output = ""; //placeholder for text output
if(filePath.files && filePath.files[0]) {
reader.onload = function (e) {
output = e.target.result;
displayContents(output);
};//end onload()
reader.readAsText(filePath.files[0]);
}//end if html5 filelist support
else if(ActiveXObject && filePath) { //fallback to IE 6-8 support via ActiveX
try {
reader = new ActiveXObject("Scripting.FileSystemObject");
var file = reader.OpenTextFile(filePath, 1); //ActiveX File Object
output = file.ReadAll(); //text contents of file
file.Close(); //close file "input stream"
displayContents(output);
} catch (e) {
if (e.number == -2146827859) {
alert('Unable to access local files due to browser security settings. ' +
'To overcome this, go to Tools->Internet Options->Security->Custom Level. ' +
'Find the setting for "Initialize and script ActiveX controls not marked as safe" and change it to "Enable" or "Prompt"');
}
}
}
else { //this is where you could fallback to Java Applet, Flash or similar
return false;
}
return true;
}
/**
* display content using a basic HTML replacement
*/
function displayContents(txt) {
var el = document.getElementById('main');
el.innerHTML = txt; //display output in DOM
}
</script>
</head>
<body onload="checkFileAPI();">
<div id="container">
<input type="file" onchange='readText(this)' />
<br/>
<hr/>
<h3>Contents of the Text file:</h3>
<div id="main">
...
</div>
</div>
</body>
</html>
It's also possible to do the same thing to support some older versions of IE (I think 6-8) using the ActiveX Object, I had some old code which does that too but its been a while so I'll have to dig it up I've found a solution similar to the one I used courtesy of Jacky Cui's blog and edited this answer (also cleaned up code a bit). Hope it helps.
Lastly, I just read some other answers that beat me to the draw, but as they suggest, you might be looking for code that lets you load a text file from the server (or device) where the JavaScript file is sitting. If that's the case then you want AJAX code to load the document dynamically which would be something as follows:
<!DOCTYPE html>
<html>
<head><meta charset="utf-8" />
<title>Read File (via AJAX)</title>
<script type="text/javascript">
var reader = new XMLHttpRequest() || new ActiveXObject('MSXML2.XMLHTTP');
function loadFile() {
reader.open('get', 'test.txt', true);
reader.onreadystatechange = displayContents;
reader.send(null);
}
function displayContents() {
if(reader.readyState==4) {
var el = document.getElementById('main');
el.innerHTML = reader.responseText;
}
}
</script>
</head>
<body>
<div id="container">
<input type="button" value="test.txt" onclick="loadFile()" />
<div id="main">
</div>
</div>
</body>
</html>

This can be done quite easily using javascript XMLHttpRequest() class (AJAX):
function FileHelper()
{
FileHelper.readStringFromFileAtPath = function(pathOfFileToReadFrom)
{
var request = new XMLHttpRequest();
request.open("GET", pathOfFileToReadFrom, false);
request.send(null);
var returnValue = request.responseText;
return returnValue;
}
}
...
var text = FileHelper.readStringFromFileAtPath ( "mytext.txt" );

Javascript doesn't have access to the user's filesystem for security reasons. FileReader is only for files manually selected by the user.

(fiddle:
https://jsfiddle.net/ya3ya6/7hfkdnrg/2/ )
Usage
Html:
<textarea id='tbMain' ></textarea>
<a id='btnOpen' href='#' >Open</a>
Js:
document.getElementById('btnOpen').onclick = function(){
openFile(function(txt){
document.getElementById('tbMain').value = txt;
});
}
Js Helper functions
function openFile(callBack){
var element = document.createElement('input');
element.setAttribute('type', "file");
element.setAttribute('id', "btnOpenFile");
element.onchange = function(){
readText(this,callBack);
document.body.removeChild(this);
}
element.style.display = 'none';
document.body.appendChild(element);
element.click();
}
function readText(filePath,callBack) {
var reader;
if (window.File && window.FileReader && window.FileList && window.Blob) {
reader = new FileReader();
} else {
alert('The File APIs are not fully supported by your browser. Fallback required.');
return false;
}
var output = ""; //placeholder for text output
if(filePath.files && filePath.files[0]) {
reader.onload = function (e) {
output = e.target.result;
callBack(output);
};//end onload()
reader.readAsText(filePath.files[0]);
}//end if html5 filelist support
else { //this is where you could fallback to Java Applet, Flash or similar
return false;
}
return true;
}

my example
<html>
<head>
<link rel="stylesheet" href="http://code.jquery.com/ui/1.11.3/themes/smoothness/jquery-ui.css">
<script src="http://code.jquery.com/jquery-1.10.2.js"></script>
<script src="http://code.jquery.com/ui/1.11.3/jquery-ui.js"></script>
</head>
<body>
<script>
function PreviewText() {
var oFReader = new FileReader();
oFReader.readAsDataURL(document.getElementById("uploadText").files[0]);
oFReader.onload = function(oFREvent) {
document.getElementById("uploadTextValue").value = oFREvent.target.result;
document.getElementById("obj").data = oFREvent.target.result;
};
};
jQuery(document).ready(function() {
$('#viewSource').click(function() {
var text = $('#uploadTextValue').val();
alert(text);
//here ajax
});
});
</script>
<object width="100%" height="400" data="" id="obj"></object>
<div>
<input type="hidden" id="uploadTextValue" name="uploadTextValue" value="" />
<input id="uploadText" style="width:120px" type="file" size="10" onchange="PreviewText();" />
</div>
Source file
</body>
</html>

This is an old question but I think in 2022 there are ES6 ways to handle this:
const $node = document.getElementById('output')
const $file = document.getElementById('file')
const processTextByLine = text => {
const arr = text.split(/\r?\n/gm)
arr.map(line => console.log(line))
}
const openFile = event => {
const input = event.target
if (!input) throw new Error('null input')
const [first] = input.files
const reader = new FileReader()
reader.onload = () => {
const text = reader.result
$node.innerText = text
processTextByLine(text)
}
reader.readAsText(first)
}
$file.onchange = openFile
<input id='file' type='file' accept='text/plain'><br>
<div id='output'>
...
</div>
If your file is encoded using UTF-8 then we can make an async call using Blob.text()
const $node = document.getElementById('output')
const $file = document.getElementById('file')
const processTextByLine = text => {
const arr = text.split(/\r?\n/gm)
arr.map(line => console.log(line))
}
const openFile = async event => {
const input = event.target
if (!input) throw new Error('null input')
const [file] = input.files
const text = await file.text()
$node.innerText = text
processTextByLine(text)
}
$file.onchange = openFile
<input id='file' type='file' accept='text/plain'><br>
<div id='output'>
...
</div>
Note:
processTextByLine() function is not needed, it just shows a case if we need to process the file line by line.

downloading a javascript blob variable as mhtml

I'm writing a google chrome extension that uses
chrome.pageCapture.saveAsMHTML(object details, function callback)
function callback (blob mhtmlData) {...};
http://code.google.com/chrome/extensions/dev/pageCapture.html
which basically stores a blob representation of an mhtml page into a variable.
Now I want to let the user download this blob variable as an mhtml file..
I tried this but is gives me a 200kb file filled with random characters.
chrome.pageCapture.saveAsMHTML({tabId: sender.tab.id}, function callback(mhtml){
var reader = new FileReader();
reader.readAsDataURL(mhtml);
reader.onload = function(e) {
window.open(e.target.result);
}
});

Following is some code that I put in a page actions popup. I left the stuff that I didnt use but commented it out for reference.
EDIT:
Using the library from https://github.com/eligrey/FileSaver.js it was easy, maybe you could look at that to see what their doing.
popup.html
<html>
<head>
<script xmlns="http://www.w3.org/1999/xhtml" type="application/ecmascript" async="" src="https://raw.github.com/eligrey/FileSaver.js/master/FileSaver.min.js"></script>
<script>
function onLoad(){
var downloadLink = document.querySelector("#MHTML");
var oFReader = new FileReader();
oFReader.onload = function (oFREvent) {
// None of the following worked
//window.open('data:application/octet-stream;'+oFREvent.target.result.slice(5));
//window.open('data:application/message/rfc822;'+oFREvent.target.result.slice(5));
//window.open(oFREvent.target.result);
};
chrome.tabs.getSelected(null, function(tab) {
chrome.pageCapture.saveAsMHTML({tabId: tab.id}, function (mhtml){
/// Works but requires user input
//downloadLink.setAttribute('download',tab.title+'.mhtml');
//downloadLink.setAttribute('href',window.webkitURL.createObjectURL(mhtml));
///Works but awful filename without extension
//window.open(window.webkitURL.createObjectURL(mhtml));
///Doesnt work
//oFReader.readAsDataURL(mhtml);
///Using https://github.com/eligrey/FileSaver.js , works great
saveAs(mhtml, tab.title+'.mhtml');
})
});
}
</script>
</head>
<body onload="onLoad();" style="width: 400px">
<a id="MHTML" href="#">Download Page As MHTML</a>
</body>
</html>

In case you want to give the file a name you could use an anchor element and set the name of the download attribute programmatically:
var reader = new FileReader();
reader.readAsDataURL(mhtml);
reader.onloadend = function(e) {
const dataUrl = e.target.result;
const a = document.createElement('a');
a.href = dataUrl;
a.download = fileName;
a.click();
}

Develop Reference

JavaScript is the programming language of the Web.

How to read file content in a javascript variable? - javascript

Solution to this helped me : How do I load the contents of a text file into a javascript variable? var client = new XMLHttpRequest(); client.open('GET', '/foo.txt'); client.onreadystatechange = function() { alert(client.responseText); } client.send();

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