javascript - 简单的ajax无法工作，可能是语法错误

Question

window.onload = function(){
  testAjax();
}

var testAjax = function(){
  var request = window.ActiveXObject ? new ActiveXObject("Microsoft.XMLHTTP") : new XMLHttpRequest();
  request.onreadystatechange = function(){
    if (request.readyState == 4){
      // Server is done
       try{
        var p = document.getElementById['a'];
        p.innerHTML = request.responseText;
         //document.write(request.responseText);
       }
       catch(e){
        document.write('More Epic Fail');
       }
    }
  }
  request.open('GET','updatethumbs.php',true);
  request.send(null);
}

Answer 1

快速浏览后:

var p = document.getElementById['a'];

应该是:

var p = document.getElementById('a');