go-back-with-backspace/is_editable.js

// Determine whether focus is in an editable text field.
function isEditable(path) {
  var target = path[0];

  // Elements may be explicitly marked as editable.
  if (target.isContentEditable)
    return true;

  // Several types of input fields are editable, but not all (e.g., checkboxes).
  var nodeName = target.nodeName;
  var nodeType = target.type;
  if (nodeName === 'TEXTAREA' ||
      (nodeName === 'INPUT' && (nodeType === 'text' ||
                                nodeType === 'email' ||
                                nodeType === 'password' ||
                                nodeType === 'search'))) {
    return true;
  }

  // Certain CSS styles, on elements or their parents, also indicate editable
  // fields.
  var pathLength = path.length;
  for (var i = 0; i < pathLength; ++i) {
    target = path[i];
    if (target.nodeType == 1) { // Only Elements have computed styles.
      var userModify = getComputedStyle(path[i])['-webkit-user-select'];
      if (userModify == 'read-write' || userModify == 'write-only')
        return true;
    }
  }
  return false;
}