Saving HTML5 textarea contents to file

I tested engincancan's answer, and it was almost there, but not quite. First of all, the file format for "ecc.plist" was not recognizable anywhere. Second of all, in order for the code to work on the desktop in Safari, Chrome, and Firefox, you have to use an existing anchor tag and not create one (document.createElement('a')). The destroyClickedElement approach only works in Chrome, because it is so forgiving and lenient. And, in order for the download to work in Firefox, you have to have document.body.appendChild(downloadLink.download);

I also had wanted to save my local storage text to a file for download and the code works on desktop for Safari, Chrome and Firefox on Mac. However, I think it is impossible in iOS to save the Blob() anywhere with Chrome or Firefox. It does work, interestingly enough in Safari. For example, I can save the text file to my Wunderlist app. Here is the link my repo on Github: The Cat Whisperer on Github gh-pages

Here is the JavaScript code:

const fileDownloadButton = document.getElementById('save');
function localStorageToFile() {
    const csv = JSON.stringify(localStorage['autosave']);
    const csvAsBlob = new Blob([csv], {type: 'text/plain'});
    const fileNameToSaveAs = 'local-storage.txt';
    const downloadLink = document.getElementById('save');
    downloadLink.download = fileNameToSaveAs;
    if (window.URL !== null) {
        // Chrome allows the link to be clicked without actually adding it to the DOM
        downloadLink.href = window.URL.createObjectURL(csvAsBlob);
        downloadLink.target = `_blank`;
    } else {
        downloadLink.href = window.URL.createObjectURL(csvAsBlob);
        downloadLink.target = `_blank`;
        downloadLink.style.display = 'none';
        // add .download so works in Firefox desktop.
        document.body.appendChild(downloadLink.download);
    }
    downloadLink.click();
}
// file download button event listener
fileDownloadButton.addEventListener('click', localStorageToFile);      

A simplified version of the code in the answers:

function download(){
    var text = document.getElementById("my-textarea").value;
    text = text.replace(/\n/g, "\r\n"); // To retain the Line breaks.
    var blob = new Blob([text], { type: "text/plain"});
    var anchor = document.createElement("a");
    anchor.download = "my-filename.txt";
    anchor.href = window.URL.createObjectURL(blob);
    anchor.target ="_blank";
    anchor.style.display = "none"; // just to be safe!
    document.body.appendChild(anchor);
    anchor.click();
    document.body.removeChild(anchor);
 }

and the html:

<textarea id="my-textarea">
   Notes here...
</textarea>
<button type="button" onclick="download()">Save</button>

That should do it.

function saveTextAsFile() {
  var textToWrite = document.getElementById('textArea').innerHTML;
  var textFileAsBlob = new Blob([ textToWrite ], { type: 'text/plain' });
  var fileNameToSaveAs = "file.txt"; //filename.extension

  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();
}

var button = document.getElementById('save');
button.addEventListener('click', saveTextAsFile);

function destroyClickedElement(event) {
  // remove the link from the DOM
  document.body.removeChild(event.target);
}

#textArea {
  display: block;
  width: 100%;
}

<textarea id="textArea" rows="3">
   Notes here...
</textarea>
<button type="button" value="save" id="save">Save</button>

JSFiddle