我正在尝试构建一个脚本,该脚本将充当本机
XMLHttpRequest
对象的代理/包装器,使我能够拦截它,修改responseText并返回到原始的onreadystatechange事件。
上下文是,如果应用程序尝试接收的数据已在本地存储中可用,则中止
XMLHttpRequest
并将本地存储的数据传递回应用程序的成功/失败回调方法。假设我无法控制应用程序现有的 AJAX 回调方法。
我最初尝试过以下想法..
var send = XMLHttpRequest.prototype.send;
XMLHttpRequest.prototype.send = function(data){
//Do some stuff in here to modify the responseText
send.call(this, data);
};
但正如我现在所确定的,responseText 是只读的。
然后我尝试后退一步,编写我自己的完整本机代理到
XMLHttpRequest
,最终编写我自己版本的本机方法。与这里讨论的类似...
http://www.ilinsky.com/articles/XMLHttpRequest/#implementation-wrapping
但是它很快就变得混乱了,并且仍然很难将修改后的数据返回到原始的
onReadyStateChange
方法中。
有什么建议吗?这可能吗?
//
// firefox, ie8+
//
var accessor = Object.getOwnPropertyDescriptor(XMLHttpRequest.prototype, 'responseText');
Object.defineProperty(XMLHttpRequest.prototype, 'responseText', {
get: function() {
console.log('get responseText');
return accessor.get.call(this);
},
set: function(str) {
console.log('set responseText: %s', str);
//return accessor.set.call(this, str);
},
configurable: true
});
//
// chrome, safari (accessor == null)
//
var rawOpen = XMLHttpRequest.prototype.open;
XMLHttpRequest.prototype.open = function() {
if (!this._hooked) {
this._hooked = true;
setupHook(this);
}
rawOpen.apply(this, arguments);
}
function setupHook(xhr) {
function getter() {
console.log('get responseText');
delete xhr.responseText;
var ret = xhr.responseText;
setup();
return ret;
}
function setter(str) {
console.log('set responseText: %s', str);
}
function setup() {
Object.defineProperty(xhr, 'responseText', {
get: getter,
set: setter,
configurable: true
});
}
setup();
}
以下脚本在通过 XMLHttpRequest.prototype.send 发送之前完美拦截数据
<script>
(function(send) {
XMLHttpRequest.prototype.send = function(data) {
this.addEventListener('readystatechange', function() {
}, false);
console.log(data);
alert(data);
};
})(XMLHttpRequest.prototype.send);
</script>
在我看来,要拦截
XMLHttpRequest
的响应,更现代的解决方案将扩展原始 XMLHttpRequest 并将其覆盖在 window
对象中:
const { interceptXhrResponse } = (function () {
let interceptionRules = [];
/**
* Function to intercept responses for given URL patterns
* @param {RegExp} urlPattern - Regular expression to match the (canonicalized) URL
* @param {Function} responseHandler - Function to handle the intercepted response
*/
function interceptXhrResponse(urlPattern, responseHandler) {
interceptionRules.push({ urlPattern, responseHandler });
}
// Function to find specific handler for the URL and return modified response
function handleInterceptedResponse(response, url) {
const interceptionRule = interceptionRules.find(({ urlPattern }) =>
urlPattern.test(url)
);
if (interceptionRule) {
const { responseHandler } = interceptionRule;
return responseHandler(response, url);
}
return response;
}
const OriginalXMLHttpRequest = window.XMLHttpRequest;
class XMLHttpRequest extends OriginalXMLHttpRequest {
get responseText() {
// If the request is not done, return the original responseText
if (this.readyState !== 4) {
return super.responseText;
}
return handleInterceptedResponse(super.responseText, this.responseURL);
}
get response() {
// If the request is not done, return the original response
if (this.readyState !== 4) {
return super.response;
}
return handleInterceptedResponse(super.response, this.responseURL);
}
}
window.XMLHttpRequest = XMLHttpRequest;
return { interceptXhrResponse };
})();
上面的代码公开了
interceptXhrResponse
函数,允许您使用正则表达式和相应的响应处理程序指定 URL 模式。您可以在处理程序中返回您想要的所有内容来更改响应。
例如:
interceptXhrResponse(/.+/, (response, url) => {
return `Response of ${url}: Intercepted. Original response length: ${String(response).length}`
})
然后我们可以尝试发起一个
XMLHttpRequest
:
const xhr = new XMLHttpRequest()
xhr.open('GET', 'https://stackoverflow.com/404')
xhr.send()
xhr.onloadend = () => {
console.log(xhr.responseText)
}
输出:
Response of https://stackoverflow.com/404: Intercepted. Original response length: 63486
您的后退是一种矫枉过正:您可以在 XMLHttpRequest 上添加您自己的 getter:(有关属性的更多信息)
Object.defineProperty(XMLHttpRequest.prototype,"myResponse",{
get: function() {
return this.responseText+"my update"; // anything you want
}
});
用途:
var xhr = new XMLHttpRequest();
...
console.log(xhr.myResponse); // xhr.responseText+"my update"
注意在现代浏览器上您可以运行
xhr.onload
(请参阅XMLHttpRequest2提示)
由于某种原因,直到最近,被接受的答案一直在 Twitter 上对我有用。所以这是另一种有效的方法:
var open_prototype = XMLHttpRequest.prototype.open
unsafeWindow.XMLHttpRequest.prototype.open = function() {
this.addEventListener('readystatechange', function(event) {
if ( this.readyState === 4 ) {
var response = event.target.responseText.replaceAll("a", "b");
Object.defineProperty(this, 'response', {writable: true});
Object.defineProperty(this, 'responseText', {writable: true});
this.response = this.responseText = response;
}
});
return open_prototype.apply(this, arguments);
};