Question

我有一个按钮点击生成的事件，它会引发XMLHttpRequest。但是，我发现一旦启动XMLHttpRequest，原始事件就会设置为null。为什么会这样？有没有办法保留原始事件？

＆＃13;

document.getElementById('start').addEventListener('click', handler);

function handler(e){
  var req = new XMLHttpRequest();
  var method = 'GET';
  var destination = 'example.com';
  req.open(method, destination);
  req.send();
  
  console.log(e.currentTarget) // shows <button></button>
  
  req.onreadystatechange = function(){
    console.log(e.currentTarget) // shows null!!! Why???
  }
}

＆＃13;

<form>
    <button id='start' type='button'>Click</button>
</form>

＆＃13;

Answer 1

试试这样：

     function handler(e){
      const buttonEvent = e;
      var req = new XMLHttpRequest();
      var method = 'GET';
      var destination = 'example.com';
      req.open(method, destination);
      req.send();

      console.log(e.currentTarget) // shows correct current target

      req.onreadystatechange = function(){
        console.log(buttonEvent);
        console.log(buttonEvent.target) 
      }
    }

为什么XMLHttpRequest会覆盖现有事件？

1 个答案: