如何从用户获取StringBuilder(How to get StringBuilder From user)

 问题是你只有一个变量xmlhttp ，它被声明为一个全局变量。 并且每次调用函数时都通过调用new XMLHttpRequest()覆盖它。 它创建一个新的，并指定回调，但随后立即通过创建一个新对象来销毁该引用。 
 
 修复是为每个请求保留一个本地XMLHttpRequest对象。 
 
function gethtml(URL, elementID){
  // using the 'var' keyword makes these variables local in scope -
  // only accessible from this function
  if (window.XMLHttpRequest) {      
    var xmlhttp=new XMLHttpRequest();
  } else {  
    var xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");   
  }

  // ... 
}
 
 使用var关键字，它应该按预期工作。 

The problem is you only have one variable xmlhttp, which is declared as a global variable. And you overwrite it by calling new XMLHttpRequest() each time the function is called. It creates a new one, and specifies the callbacks, but then immediately goes and destroys that reference by creating a new object.
 
The fix is to keep a local XMLHttpRequest object for each request. 
 
function gethtml(URL, elementID){
  // using the 'var' keyword makes these variables local in scope -
  // only accessible from this function
  if (window.XMLHttpRequest) {      
    var xmlhttp=new XMLHttpRequest();
  } else {  
    var xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");   
  }

  // ... 
}
 
Use the var keyword and it should work as expected.