Including jQuery condition if in page have jQuery or not

// Including jQuery conditionnally.
  if (typeof jQuery === 'undefined') {
    document.write("\u003cscript src=\"\/\/ajax.googleapis.com\/ajax\/libs\/jquery\/1\/jquery.min.js\" type=\"text\/javascript\"\u003e\u003c\/script\u003e");
    document.write('<script type="text/javascript">jQuery.noConflict();<\/script>');
  }