FileSaver in HTML5

HTML

<div><input type="button" id="savetext" value="Save"/></div>
<textarea id="sometext">Hello World!</textarea>

CSS

#savetext {
  width: 40px;
}

JavaScript

function doSave() {
  var blobBuilder = window.BlobBuilder || window.MozBlobBuilder ||
                    window.WebKitBlobBuilder || window.MSBlobBuilder;
  var bb = new blobBuilder();
  bb.append(textout.value);
  var blob = bb.getBlob(); 
  var fileSaver = new FileSaver(blob);
  fileSaver.onwriteend = function(){alert("done!");};
}
var savebtn = document.getElementById("savetext"),
    textout = document.getElementById("sometext");
savebtn.addEventListener("click", doSave, false);