Set the text value of a node or element

Equivalent to `node.textContent = value` in the browser
function setTextContent(node, value) {
  if (isCommentNode(node)) {
    node.data = value;
  } else if (isTextNode(node)) {
    node.value = value;
  } else {
    var tn = newTextNode(value);
    tn.parentNode = node;
    node.childNodes = [tn];
  }
}