javascript - Ajax 和范围问题

Question

我在 AJAX 和数据范围方面遇到了一些问题。我是 Javascript 新手，我不知道如何解决我的问题。

  var urlList = new Array();
  $.ajax({
      url: "http://localhost:3000/url",
      success: function(data) {
         alert(data.expressions.url); //This shows the correct result
         urlList[0] = obj.expressions.dom;
      }
  });

  alert(urlList[0]); //this shows undefined

我需要 urlList[0] 中的数据，以便稍后使用它。我认为这是一个范围问题。

有人能给我指出正确的方向吗？

谢谢

Answer 1

这不是范围问题，而是时间问题。 ajax方法是异步执行的。这意味着调用它不会导致您的程序等待它完成。这会导致在请求完成之前显示警报。

要解决此问题，请将请求也放入成功函数中。这是处理请求结果的正确位置。

var urlList = new Array();

$.ajax({
    url: "http://localhost:3000/url",
    success: function(data) {

        alert(data.expressions.url); //This shows the correct result

        urlList[0] = obj.expressions.dom;

        // This might work now, depending on what `obj.expressions.dom` is. This
        // isn't becoming clear from your code. Usually you would use the `data`
        // parameter of the success function, which contains the response body of
        // the ajax request that has just finished.
        alert(urlList[0]);

        // of course you can call other functions as well. For instance, you 
        // could call
        urlListChanged();
        // ..which you can declare in global scope. This way, you can repond to 
        // changes  from multiple sources, without having to duplicate code.
        // It will all work, as long as you use the success handler as the trigger.
    }
});


function urlListChanged()
{
   alert(urlList[0]);
}