Takes a window selection and downloads a plaintext file.

getPlainText.js

var text = "";
  function getPlainText() {
    if(window.getSelection == undefined) {
      alert("There is no text selected. Please select some text from the page and try again.")
    } else {
      text = window.getSelection().toString();
      console.log(text);

      var download = document.getElementById('download');
      download.href = 'data:text/plain;charset:utf-8,' + encodeURIComponent(text);
      var event = new MouseEvent('click');
      download.dispatchEvent(event);
      }
    return text;
  }