highlight_share.js

var savedText = null; // Variable to save the text

function saveSelection() {
  if (window.getSelection) {
    var sel = window.getSelection();
    if (sel.getRangeAt && sel.rangeCount) {
      return sel.getRangeAt(0);
    }
  } else if (document.selection && document.selection.createRange) {
    return document.selection.createRange();
  }
  return null;
}

function restoreSelection(range) {
  if (range) {
    if (window.getSelection) {
      var sel = window.getSelection();
      sel.removeAllRanges();
      sel.addRange(range);
    } else if (ddocument.selection && range.select) {
      range.select();
    }
  }
}

var btnWrap = document.getElementById('share-button'),
    btnShare = btnWrap.children[0];

document.onmouseup = function(e) {

  savedText = saveSelection(); // Save selection on mouse-up

  setTimeout(function() {

    var isEmpty = savedText.toString().length === 0; // Check selection text length

    // set sharing button position
    btnWrap.style.top = (isEmpty ? -9999 : e.pageY) + 'px';
    btnWrap.style.left = (isEmpty ? -9999 : e.pageX) + 'px';

  }, 10);

};

btnShare.onmousedown = function(e) {

  if (!savedText) return;

  window.open('https://twitter.com/intent/tweet?text=' + savedText, 'shareWindow', 'width=300,height=150,top=50,left=50'); // Insert the selected text into sharing URL
  restoreSelection(savedText); // select back the old selected text

  // hide if we are done
  setTimeout(function() {
    btnWrap.style.top = '-9999px';
    btnWrap.style.left = '-9999px';
  }, 1000);

  return false;

};