I would like to write a small html file that would run locally and manipulate a small text file on my computer. My requirements are:
Is this possible at all? If yes, how do I read and write my text file using javascript?
As is being discussed in Itay Moav's answer, writing to a local file with a local HTML file is perhaps going to be an issue without running in an elevated privilege mode and having additional Javascript capabilities (that allow you to save local files).
However, accessing a local file from an HTML file is entirely possible. Below is some example code.
mytext.txt
My local text file
local.html
<html>
<head>
<base href="file:///C:/path/to/your/folder/"/>
<script>
window.onload = function(){
var iframe = document.createElement('iframe');
iframe.id = 'iframe';
iframe.style.display = 'none';
document.body.appendChild(iframe);
iframe.src = 'mytext.txt';
setTimeout(function(){
var text = document.getElementById('iframe').contentDocument.body.firstChild.innerHTML;
alert(text);
}, 1000);
}
</script>
</head>
<body>
<h1>Hello World!</h1>
</body>
</html>
This will make an alert 1 second after the html page loads (to allow the iframe to load first), and will contain the content within the mytext.txt file.
Note, if it's plaintext, Firefox will wrap it with a PRE element, which is why I did firstChild. Also, note the use of the BASE element, which points to your local directory with your files.
The example given by Jared works fine. However setting an unknown watiting time is not atractive. Instead attach an onload event to the iframe calling a function reading the contents of the text-file an doing whatever as soon as possible.
Here is a revised example:
<html>
<head>
<script>
function readfile() {
alert(document.getElementById('iframe').contentDocument.body.firstChild.innerHTML);
}
</script>
</head>
<body>
<iframe id='iframe' src = 'test.txt' onload='readfile()'> </iframe>
<h1>Hello World!</h1>
</body>
</html>
The file test.txt off course has to exist in the same directory as the above html file itself.
Normally, it is not possible and would be a security issue.
How ever, if you use some plugins (ActiveX, FF extensions etc) they may enable you to do so.
There is also the subject of local storage you can use with the most newer browsers.
From your comments, I am wondering why not using PHP/Ruby any other server side language to do so? They are tailored just for that.
You can also use an hta file extension and it will load in IE where you have access to ActiveX objects. In a pinch you can very quickly get an executable program up and running with minimal effort.
The relevant code is:
<!DOCTYPE html>
<html>
<head>
<HTA:APPLICATION
ID="somethingHere"
APPLICATIONNAME="YouAppsName"
WINDOWSTATE="maximize"
>
<script language="JScript">
function ReadFile(filename) {
try {
var fso = new ActiveXObject("Scripting.FileSystemObject");
var fh = fso.OpenTextFile(filename, 1);
var contents = fh.ReadAll();
fh.Close();
return contents;
} catch (Exception) {
return "Cannot open file :(";
}
function WriteFile(filename, text) {
try {
var fso = new ActiveXObject("Scripting.FileSystemObject");
var fh = fso.OpenTextFile(filename, 8, true);
fh.Write(text);
fh.Close();
} catch(Exception) {
alert("Failed to write.");
}
}
.....
</script>
etc.....
Whey not use the fetch() function?
Mind you he is going to serve the file using another server
Here is a tutorial of a guy using it https://youtu.be/C3dfjyft_m4
