在JavaScript中从服务器获取响应

Question

如何使用JavaScript从服务器获得响应？ 这是我的示例代码：

function get_Image(values) {
    if (window.XMLHttpRequest) {
        var http_request = new XMLHttpRequest();
    } else if (window.ActiveXObject) {
        var http_request = new ActiveXObject("Microsoft.XMLHTTP");
    } else {
        http_request.open("GET", "http://sample_address_for_server", true);
        http_request.send();
    }
    alert(http_request.status);
    if (http_request.readyState == 4) {
        if (http_request.status == 200) {
            xmlDoc = http_request.responseText;
            alert(xmlDoc);
        }
    }
}

Answer 1

尝试使用此块..您的代码的问题是在创建开放连接时错过了引号

function get_Image(values){ 

      var http_request = false;
      if (window.XMLHttpRequest) {
        http_request = new XMLHttpRequest()
      } else {
        if (window.ActiveXObject) {
          try {
            http_request = new ActiveXObject("MSXML2.XMLHTTP")
          } catch () {
            try {
              http_request = new ActiveXObject("Microsoft.XMLHTTP")
            } catch () {}
          }
        } else {
          return false
        }
      }
      http_request.onreadystatechange = function () {

       alert(http_request.status);    
          if ( http_request.readyState == 4 ) {    
         if ( http_request.status == 200 ) {    
        xmlDoc = http_request.responseText;    
            alert(xmlDoc);   
    }}
      };
     http_request.open( "GET", "http://sample_address_for_server", true);
        http_request.send(null);   
    }

Answer 2

您必须将一个函数附加到对象的onreadystatechange事件。 您正在做的方式是，在发送请求后立即尝试获取响应，但是您还没有任何响应。

function get_Image(values) {
    if (window.XMLHttpRequest) {
        var http_request = new XMLHttpRequest();
    } else if (window.ActiveXObject) {
        var http_request = new ActiveXObject("Microsoft.XMLHTTP");
    } else {
        http_request.open("GET", "http://sample_address_for_server", true);
        http_request.send();
    }
    alert(http_request.status);
    http_request.onreadystatechange = function(){
       if (http_request.readyState == 4) {
           if (http_request.status == 200) {
               xmlDoc = http_request.responseText;
               alert(xmlDoc);
           }
       }
    }
}