Failed to execute 'setRequestHeader' on 'XMLHttpRequest': The object's state must be OPENED.

在設置請求頭的時候報這個Failed to execute 'setRequestHeader' on 'XMLHttpRequest': The object's state must be OPENED.，是由於需要先打開XMLHttpRequest

 var xhr = new XMLHttpRequest();
//打開xhr
  xhr.open('GET',url );
//設置請求頭，請求頭的設置必須在xhr打開之后，並且在send之前
 xhr.setRequestHeader('user-sessionid', sessionId);