Develop Reference

File manipulations such as Read/Write local files using Javascript without server

I'm just trying on the task, file manipulation system using java script. As I was referred from W3C File API( https://www.w3.org/TR/FileAPI/ ), we can only read local files like
var file = "test.txt";
function readTextFile(file) {
var readFile;
if(window.XMLHttpRequest){
// for new browsers
readFile = new XMLHttpRequest();
}else{
//for old browsers like IE5 or IE6
readFile = new ActiveXObject("Microsoft.XMLHTTP");
}
readFile.open("GET", file, true);
readFile.onreadystatechange = function() {
if(readFile.readyState === 4) {
if(readFile.status === 200 || readFile.status == 0) {
//text will be displayed that read from the file
console.log(readFile.responseText);
}
}
}
readFile.send(null);
}
but it looks there is no options to write on file without server. I was tried to fetch solutions from the websites like http://www.stackoverflow.com/, the study says almost there is no possibilities.
For an example what I got is
from https://gist.github.com/Arahnoid/9925725
It shows error "TypeError: file.open is not a function."
So my question is, Is there any possible to file manipulations(asking only about Write file) for local files without using server-side scripting or is any extensions like available?
We can do file manipulations using server scripting languages such as PHP, Node.js.
Thanks in advance.

In your code, it's not reading from the local file (test.txt), it's sending Ajax GET request to server and read file in server side.
To read local file (files that stored in machine where browser is installed), you need to use FileAPI, which is not used in current code.
To write file to local, it's impossible to write it directly using JavaScript. Otherwise, it would be a huge security vulnerability. However, you can generate a URL from File object, and use that URL as the href attribute of <a> tag, so that user can download and "write to local" manually.
Here is a code snippet to read & "write" local file:
var inputElement = document.getElementById("input");
var reader = new FileReader();
var downloadLink = document.getElementById('downloadLink');
reader.onloadend = function(){
console.log(reader.result);
}
inputElement.addEventListener("change", handleFiles, false);
function handleFiles() {
var fileSelected = this.files[0]; /* now you can work with the file list */
reader.readAsBinaryString(fileSelected);
downloadLink.href = window.URL.createObjectURL(fileSelected);
}
<input type="file" id="input">
<a id="downloadLink" download>Download</a>

Using Google Chrome extensions to import/export JSON files?

I'm creating a Google Chrome extension at the moment and I was wondering if it's possible for it to both create JSON files to download (export) and create a button where users can make the extension open and parse JSON files that they have saved in their local file system or on a USB stick (import)?
The parsing of each JSON from the local file system would simply involve reading off each key-value pair and doing something with the data. It would only have to deal with strings, so nothing complicated.
**EDIT: **My question is not a duplicate of this one because I'm not interested in changing the user's download path. All I want is to enable them to, with their consent, download a file to their normal download directory (which Filesaver.js can do). Plus, that post says nothing about importing.

You can fake link to "download" imaginary array MyData or whatever,:
var MyArray = [elem1, elem2, ....];
var _myArray = JSON.stringify(MyArray , null, 4); //indentation in json format, human readable
var vLink = document.createElement('a'),
vBlob = new Blob([_myArray], {type: "octet/stream"}),
vName = 'watever_you_like_to_call_it.json',
vUrl = window.URL.createObjectURL(vBlob);
vLink.setAttribute('href', vUrl);
vLink.setAttribute('download', vName );
vLink.click();
this will export/download your array into json file named as vName variable.
If you wish to import/read file:
create input element (type=file) and make it invisible (here I'm having html element and then adding js listener in script)
<input type="file" id="importOrig" accept=".json" style="display:none"/>
script
importOrig.addEventListener("change", importFun, false);
make button fakeImp (or any element), that you can style as you wish and that will be used as trigger for importing event
fakeImp.onclick = function () {importOrig.click()}
import function (from listener)
function importFun(e) {
var files = e.target.files, reader = new FileReader();
reader.onload = _imp;
reader.readAsText(files[0]);
}
function _imp() {
var _myImportedData = JSON.parse(this.result);
//here is your imported data, and from here you should know what to do with it (save it to some storage, etc.)
......
importOrig.value = ''; //make sure to clear input value after every import
}

Javascript new File() gem file size

I have the following file structure:
test.html
test.json
And the following JS function:
function get_file(){
var app_path = app.activeDocument.path,
file = new File(app_path + '/test.json');
console.log(file);
}
How can I make the function log the file's content?

I'm not sure if everything you can do in the browsers environment translates to everything you can do in photoshops environment. But you should look at a few things.
Doing This in the Browser
The File object.
https://developer.mozilla.org/en-US/docs/Web/API/File
Notable that it extends the Blob object.
https://developer.mozilla.org/en-US/docs/Web/API/Blob
Which if you researched you would find it can be read using the FileReader.
https://developer.mozilla.org/en-US/docs/Web/API/FileReader
So this would work in the browser but may/may-not work in the photoshop scripting set.
function get_file(){
var app_path = app.activeDocument.path,
file = new File(app_path + '/test.json');
var reader = new FileReader();
reader.onloadend = function() {
console.log(reader.result);
}
reader.readAsText(file);
}
This is asynchronous so you may need to use a callback depending on what you're trying to do with this. You won't be able to return the string from inside the reader.onloadend event.
Doing This in Photoshop
Take a look at their scripting references. Specifically the javascript reference.
All Resources: http://www.adobe.com/devnet/photoshop/scripting.html
Javascript PDF: http://wwwimages.adobe.com/content/dam/Adobe/en/devnet/photoshop/pdfs/photoshop-cc-javascript-ref-2015.pdf
It looks like they don't have the FileReader but instead the File object can be used to read content. The File API begins on page 109 but it's empty! The documentation is a bit pathetic so I can see why you'd have trouble finding this. With some searching I found someone doing this in 2012 (but I don't know if it will still work- worth a shot)
var b = new File("c:\test.txt");
b.open('r');
var str = "";
while(!b.eof) {
str += b.readln();
}
b.close();
alert(str);
Let me know if that works.

Parse a local file to an array using JavaScript

I am trying to read a local file and have each line as an index in an array using JavaScript. I have been searching for the past 20 minutes and either I'm stupid or there really isn't an answer that pertains to my problem (...but it's probably the former :P). I am really new to JavaScript so if you have an answer could you please comment the code just to I know what's going on?
Also, from the searching I've done on the internet some people said JavaScript can't read local file for security reasons so if that is correct is there another language I can use? I'm a bit familiar with PHP if that is an option, which I doubt it is.
EDIT
As per thg435's question, I'll explain what I am trying to accomplish.
My project is to analyze a BUNCH of water quality data that has been collected by the Ontario gov't (which I've done) and display it in some way. I have chosen to display it on a webpage using the Google Maps API. I currently have a file of chemicals that were found. Each line is a different chemical. I would like to read the file in an array then create an option menu displaying the chemicals in the array.
Also, the local file I would like to read will the be the same name and location all the time. I have seen people have boxes where the user clicks and chooses their file or to drag and drop but that's not what I'm looking for.
I don't think I explained this properly. I have a file in the same directory as my HTML and JavaScript files that contains words. Example:
Line 1: "Iron"
Line 2: "Aluminum"
Line 3: "Steel"
etc...
I would like to read the file and parse each line into a different index in an array. I don't want the user to be able to choose which file to read using the <input ... /> thing.

You're going to want to take a look at the FileReader API. This should allow you to read the text of a local file via readAsText(). This won't work in every browser but should work in all modern browser. You can see which browsers support it here.
Example:
<input id="file" type="file" />
var filesInput = document.getElementById("file");
filesInput.addEventListener("change", function (event) {
var files = event.target.files;
var file = files[0];
var reader = new FileReader();
reader.addEventListener("load", function (event) {
var textFile = event.target;
alert(textFile.result);
});
reader.readAsText(file);
});
It's not possible to invoke the FileReader API without user interaction. Consequently, your user would have to select whatever file to load in order for it to be read in pure JS. Since I'm assuming this will be up on a server, why not just put the list of chemicals also up on the server and GET the JSON encoded array of the results. Then you can decode them with Javascript.

You can access local files in 2 ways that I know of. The first way is making the user drag-and-drop the files onto the page, and using an <input type="file"> tag.
For the former, you would need to do the following:
addEventListener('dragover', function(e){e.preventDefault();});
addEventListener('drop', function(e) {
eventHandler.call(e.dataTransfer||e.clipboardData);
e.preventDefault();
});
For the latter, you'd need to add an event listener for the change event on the input:
document.getElementById('upload').addEventListener('change', eventHandler)
And for both, you'd need to have this as a basic callback function:
function eventHandler() {
var file = this.files[0]; //get the files
var reader = new FileReader(); //initiate reader
reader.onloadend = callbackFn; //set event handler
reader.readAsText(file); //initiate reading of files
if (this.id) { //only run if this is the input
var id = this.id;
this.outerHTML = this.outerHTML; //this resets the input
document.getElementById(id).addEventListener('change', eventHandler); //reattach event handler
}
function callbackFn(e) {
document.getElementById('output').value = e.target.result; //output it to a textarea
}
}
Here is a demo where the text contents (that what you see when opening it in notepad) of any file you drop in it, or any file you select from the input, is put in the textarea.
For more information, see https://developer.mozilla.org/en-US/docs/Using_files_from_web_applications.

Reading client side text file using Javascript

I want to read a file (on the client side) and get the content in an array. It will be just one file. I have the following and it doesn't work. 'query_list' is a textarea where I want to display the content of the file.
<input type="file" id="file" name="file" enctype="multipart/form-data"/>
<script>
document.getElementById('file').addEventListener('change', readFile, false);
function readFile (evt) {
var files = evt.target.files;
var file = files[0];
var fh = fopen(file, 0);
var str = "";
document.getElementById('query_list').textContent = str;
if(fh!=-1) {
length = flength(fh);
str = fread(fh, length);
fclose(fh);
}
document.getElementById('query_list').textContent = str;
}
</script>
How should I go about it? Eventually I want to loop over the array and run some SQL queries.

If you want to read files on the client using HTML5's FileReader, you must use Firefox, Chrome or IE 10+. If that is true, the following example reads a text file on the client.
your example attempts to use fopen that I have never heard of (on the client)
http://jsfiddle.net/k3j48zmt/
document.getElementById('file').addEventListener('change', readFile, false);
function readFile (evt) {
var files = evt.target.files;
var file = files[0];
var reader = new FileReader();
reader.onload = function(event) {
console.log(event.target.result);
}
reader.readAsText(file)
}
For IE<10 support you need to look into using an ActiveX Object like ADO.Stream Scripting.FileSystemObject http://msdn.microsoft.com/en-us/library/2z9ffy99(v=vs.85).aspx but you'll run into a security problem. If you run IE allowing all ActiveX objects (for your website), it should work.

There is such thing as HTML5 File API to access local files picked by user, without uploading them anywhere.
It is quite new feature, but supported by most of modern browsers.
I strongly recommend to check out this great article to see, how you can use it.
There is one problem with this, you can't read big files (~400 MB and larger) because straight forward FileAPI functions attempting to load entire file into memory.
If you need to read big files, or search something there, or navigate by line index check my LineNavigator, which allows you to read, navigate and search in files of any size. Try it in jsFiddle! It is super easy to use:
var navigator = new FileNavigator(file);
navigator.readSomeLines(0, function linesReadHandler(err, index, lines, eof, progress) {
// Some error
if (err) return;
// Process this line bucket
for (var i = 0; i < lines.length; i++) {
var line = lines[i];
// Do something with it
}
// End of file
if (eof) return;
// Continue reading
navigator.readSomeLines(index + lines.length, linesReadHandler);
});

Well I got beat to the answer but its different:
<input type="file" id="fi" />
<button onclick="handleFile(); return false;">click</button>
function handleFile() {
var preview = document.getElementById('prv')
var file = document.getElementById('fi').files[0];
var div = document.body.appendChild(document.createElement("div"));
div.innerHTML = file.getAsText("utf-8");
}
This will work in FF 3.5 - 3.6, and that's it. FF 4 and WebKit you need to use the FileReader as mentioned by Juan Mendes.
For IE you may find a Flash solution.

I work there, but still wanted to contribute because it works well: You can use the filepicker.io read api to do exactly this. You can pass in an dom element and get the contents back, for text or binary data, even in IE8+