Download textarea contents as a file using only Javascript (no server-side)

I am being asked to make a "download" button that downloads the contents of a textarea on the same page as a file, with the browser's "Save As..." dialog showing up. Copy/paste would do the job just fine, but it is a "requirement".

Right now, I am just posting the contents of the textarea to the server, which echos them back with Content-disposition: attachment slapped on. Is there a way to do this with just client-side Javascript?

This may be what you are looking for: http://thiscouldbebetter.wordpress.com/2012/12/18/loading-editing-and-saving-a-text-file-in-html5-using-javascrip/

It uses the browser's download dialogue, but supports only FF and Chrome, and maybe more browsers now?

   function saveTextAsFile(textToWrite, fileNameToSaveAs)
    {
    	var textFileAsBlob = new Blob([textToWrite], {type:'text/plain'}); 
    	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();
    }

<textarea id=t>Hey</textarea><br>
<button onclick=saveTextAsFile(t.value,'download.txt')>Download</button>

I found a simple solution here: https://codepen.io

My text area:<br />
<textarea rows='10' cols='80' id='myTextArea' ></textarea>

<br /><br />

Download button: <br />
<input value='download' type='button'
onclick='doDL(document.getElementById("myTextArea").value)' />


<script type='text/javascript'>
function doDL(s){
    function dataUrl(data) {return "data:x-application/text," + escape(data);}
    window.open(dataUrl(s));
}
</script>

Hope it will help.

You could try window.location = "data:application/octet-stream,"+text but that doesn't provide a mechanism through which you can suggest a name, and also IE has a very small cap on the maximum length of a data URI which could be a problem.