javascript 中的以下代码给了我错误“this.callback 不是一个函数
function ajaxRequest()
{
var httpObject;
this.open = open;
this.callback = function(){};
function getHTTPObject()
{
if (window.ActiveXObject)
return new ActiveXObject("Microsoft.XMLHTTP");
else if (window.XMLHttpRequest)
return new XMLHttpRequest();
else
{
alert("Your browser does not support AJAX.");
return null;
}
}
function onstatechange()
{
if(httpObject.readyState == 4)
{
this.callback(httpObject.responseText);
}
}
function open(url, callback)
{
httpObject = getHTTPObject();
if (httpObject != null)
{
httpObject.open("GET", url, true);
httpObject.send(null);
this.callback = callback;
httpObject.onreadystatechange = onstatechange;
}
}
}
为什么 open 方法不将回调参数视为函数?
如果是的话为什么我不能在 onstatechange 函数中调用它?
我该如何进行这项工作?
原因是因为onstatechange
被作为事件处理程序调用,并且this
指针可能指向触发事件的对象,而不是ajaxRequest
对象,如您所料。
下面的重写存储了this
变量中的变量称为that
在 onstatechange() 函数可以访问的执行上下文中。这应该可以解决问题。
总而言之,如果您没有彻底理解 Javascript 闭包和执行上下文,即使您了解,使用框架来执行 AJAX 请求也会好得多。 jQuery 和 Prototype 是不错的选择。
function ajaxRequest()
{
var httpObject;
this.open = open;
this.callback = function(){};
var that = this;
function getHTTPObject()
{
if (window.ActiveXObject)
return new ActiveXObject("Microsoft.XMLHTTP");
else if (window.XMLHttpRequest)
return new XMLHttpRequest();
else
{
alert("Your browser does not support AJAX.");
return null;
}
}
function onstatechange()
{
if(httpObject.readyState == 4)
{
that.callback(httpObject.responseText);
}
}
function open(url, callback)
{
httpObject = getHTTPObject();
if (httpObject != null)
{
httpObject.open("GET", url, true);
httpObject.send(null);
this.callback = callback;
httpObject.onreadystatechange = onstatechange;
}
}
}
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