Is it possible to write data to file using only JavaScript?

I want to Write Data to existing file using JavaScript. I don't want to print it on console. I want to Actually Write data to abc.txt. I read many answered question but every where they are printing on console. at some place they have given code but its not working. So please can any one help me How to actually write data to File.

I referred the code but its not working: its giving error:

>Uncaught TypeError: Illegal constructor

on chrome and

>SecurityError: The operation is insecure.

on Mozilla

var f = "sometextfile.txt";

writeTextFile(f, "Spoon")
writeTextFile(f, "Cheese monkey")
writeTextFile(f, "Onion")

function writeTextFile(afilename, output)
{
  var txtFile =new File(afilename);
  txtFile.writeln(output);
  txtFile.close();
}

So can we actually write data to file using only Javascript or NOT?

You can create files in browser using Blob and URL.createObjectURL. All recent browsers support this.

You can not directly save the file you create, since that would cause massive security problems, but you can provide it as a download link for the user. You can suggest a file name via the download attribute of the link, in browsers that support the download attribute. As with any other download, the user downloading the file will have the final say on the file name though.

var textFile = null,
  makeTextFile = function (text) {
    var data = new Blob([text], {type: 'text/plain'});

    // If we are replacing a previously generated file we need to
    // manually revoke the object URL to avoid memory leaks.
    if (textFile !== null) {
      window.URL.revokeObjectURL(textFile);
    }

    textFile = window.URL.createObjectURL(data);

    // returns a URL you can use as a href
    return textFile;
  };

Here's an example that uses this technique to save arbitrary text from a textarea.

If you want to immediately initiate the download instead of requiring the user to click on a link, you can use mouse events to simulate a mouse click on the link as Lifecube's answer did. I've created an updated example that uses this technique.

  var create = document.getElementById('create'),
    textbox = document.getElementById('textbox');

  create.addEventListener('click', function () {
    var link = document.createElement('a');
    link.setAttribute('download', 'info.txt');
    link.href = makeTextFile(textbox.value);
    document.body.appendChild(link);

    // wait for the link to be added to the document
    window.requestAnimationFrame(function () {
      var event = new MouseEvent('click');
      link.dispatchEvent(event);
      document.body.removeChild(link);
	});
    
  }, false);

Some suggestions for this -

1. If you are trying to write a file on client machine, You can't do this in any cross-browser way. IE does have methods to enable "trusted" applications to use ActiveX objects to read/write file.
2. If you are trying to save it on your server then simply pass on the text data to your server and execute the file writing code using some server side language.
3. To store some information on the client side that is considerably small, you can go for cookies.
4. Using the HTML5 API for Local Storage.

If you are talking about browser javascript, you can not write data directly to local file for security reason. HTML 5 new API can only allow you to read files.

But if you want to write data, and enable user to download as a file to local. the following code works:

    function download(strData, strFileName, strMimeType) {
	var D = document,
		A = arguments,
		a = D.createElement("a"),
		d = A[0],
		n = A[1],
		t = A[2] || "text/plain";

	//build download link:
	a.href = "data:" + strMimeType + "charset=utf-8," + escape(strData);


	if (window.MSBlobBuilder) { // IE10
		var bb = new MSBlobBuilder();
		bb.append(strData);
		return navigator.msSaveBlob(bb, strFileName);
	} /* end if(window.MSBlobBuilder) */



	if ('download' in a) { //FF20, CH19
		a.setAttribute("download", n);
		a.innerHTML = "downloading...";
		D.body.appendChild(a);
		setTimeout(function() {
			var e = D.createEvent("MouseEvents");
			e.initMouseEvent("click", true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
			a.dispatchEvent(e);
			D.body.removeChild(a);
		}, 66);
		return true;
	}; /* end if('download' in a) */



	//do iframe dataURL download: (older W3)
	var f = D.createElement("iframe");
	D.body.appendChild(f);
	f.src = "data:" + (A[2] ? A[2] : "application/octet-stream") + (window.btoa ? ";base64" : "") + "," + (window.btoa ? window.btoa : escape)(strData);
	setTimeout(function() {
		D.body.removeChild(f);
	}, 333);
	return true;
}

to use it:

download('the content of the file', 'filename.txt', 'text/plain');

Try

let a = document.createElement('a');
a.href = "data:application/octet-stream,"+encodeURIComponent("My DATA");
a.download = 'abc.txt';
a.click();

If you want to download binary data look here

Update

2020.06.14 I upgrade Chrome to 83.0 and above SO snippet stop works (reason: sandbox security restrictions) - but JSFiddle version works - here

Above answer is useful but, I found code which helps you to download text file directly on button click. In this code you can also change filename as you wish. It's pure javascript function with HTML5. Works for me!

function saveTextAsFile()
{
	var textToWrite = document.getElementById("inputTextToSave").value;
	var textFileAsBlob = new Blob([textToWrite], {type:'text/plain'});
	var fileNameToSaveAs = document.getElementById("inputFileNameToSaveAs").value;
      var downloadLink = document.createElement("a");
	downloadLink.download = fileNameToSaveAs;
	downloadLink.innerHTML = "Download File";
	if (window.webkitURL != null)
	{
		// Chrome allows the link to be clicked
		// without actually adding it to the DOM.
		downloadLink.href = window.webkitURL.createObjectURL(textFileAsBlob);
	}
	else
	{
		// Firefox requires the link to be added to the DOM
		// before it can be clicked.
		downloadLink.href = window.URL.createObjectURL(textFileAsBlob);
		downloadLink.onclick = destroyClickedElement;
		downloadLink.style.display = "none";
		document.body.appendChild(downloadLink);
	}

	downloadLink.click();
}

In the case it is not possibile to use the new Blob solution, that is for sure the best solution in modern browser, it is still possible to use this simpler approach, that has a limit in the file size by the way:

function download() {
                var fileContents=JSON.stringify(jsonObject, null, 2);
                var fileName= "data.json";
                
                var pp = document.createElement('a');
                pp.setAttribute('href', 'data:text/plain;charset=utf-8,' + encodeURIComponent(fileContents));
                pp.setAttribute('download', fileName);
                pp.click();
            }
            setTimeout(function() {download()}, 500);

$('#download').on("click", function() {
  function download() {
    var jsonObject = {
      "name": "John",
      "age": 31,
      "city": "New York"
    };
    var fileContents = JSON.stringify(jsonObject, null, 2);
    var fileName = "data.json";

    var pp = document.createElement('a');
    pp.setAttribute('href', 'data:text/plain;charset=utf-8,' + encodeURIComponent(fileContents));
    pp.setAttribute('download', fileName);
    pp.click();
  }
  setTimeout(function() {
    download()
  }, 500);
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button id="download">Download me</button>

const data = {name: 'Ronn', age: 27};              //sample json
const a = document.createElement('a');
const blob = new Blob([JSON.stringify(data)]);
a.href = URL.createObjectURL(blob);
a.download = 'sample-profile';                     //filename to download
a.click();

Check Blob documentation here - Blob MDN to provide extra parameters for file type. By default it will make .txt file

Use the code by the user @useless-code above (https://stackoverflow.com/a/21016088/327386) to generate the file. If you want to download the file automatically, pass the textFile that was just generated to this function:

var downloadFile = function downloadURL(url) {
    var hiddenIFrameID = 'hiddenDownloader',
    iframe = document.getElementById(hiddenIFrameID);
    if (iframe === null) {
        iframe = document.createElement('iframe');
        iframe.id = hiddenIFrameID;
        iframe.style.display = 'none';
        document.body.appendChild(iframe);
    }
    iframe.src = url;
}

I found good answers here, but also found a simpler way.

The button to create the blob and the download link can be combined in one link, as the link element can have an onclick attribute. (The reverse seems not possible, adding a href to a button does not work.)

You can style the link as a button using bootstrap, which is still pure javascript, except for styling.

Combining the button and the download link also reduces code, as fewer of those ugly getElementById calls are needed.

This example needs only one button click to create the text-blob and download it:

<a id="a_btn_writetofile" download="info.txt" href="#" class="btn btn-primary" 
   onclick="exportFile('This is some dummy data.\nAnd some more dummy data.\n', 'a_btn_writetofile')"
>
   Write To File
</a>

<script>
    // URL pointing to the Blob with the file contents
    var objUrl = null;
    // create the blob with file content, and attach the URL to the downloadlink; 
    // NB: link must have the download attribute
    // this method can go to your library
    function exportFile(fileContent, downloadLinkId) {
        // revoke the old object URL to avoid memory leaks.
        if (objUrl !== null) {
            window.URL.revokeObjectURL(objUrl);
        }
        // create the object that contains the file data and that can be referred to with a URL
        var data = new Blob([fileContent], { type: 'text/plain' });
        objUrl = window.URL.createObjectURL(data);
        // attach the object to the download link (styled as button)
        var downloadLinkButton = document.getElementById(downloadLinkId);
        downloadLinkButton.href = objUrl;
    };
</script>

Yes its possible Here the code is

const fs = require('fs') 
let data = "Learning how to write in a file."
fs.writeFile('Output.txt', data, (err) => { 
      
    // In case of a error throw err. 
    if (err) throw err; 
})