How can I create a XMLHttpRequest wrapper/proxy?

These methods that come to mind, what are the pros and cons of each?

Method 1: Augment native instance

var _XMLHttpRequest = XMLHttpRequest;
XMLHttpRequest = function() {
    var xhr = new _XMLHttpRequest();

    // augment/wrap/modify here
    var _open = xhr.open;
    xhr.open = function() {
        // custom stuff
        return _open.apply(this, arguments);
    }

    return xhr;
}

Method 2: Sub-"class" native XMLHttpRequest

var _XMLHttpRequest = XMLHttpRequest;
XMLHttpRequest = function() {
    // definePropertys here etc
}

XMLHttpRequest.prototype = new _XMLHttpRequest());
// OR
XMLHttpRequest.prototype = Object.create(_XMLHttpRequest);

// custom wrapped methods on prototype here
XMLHttpRequest.prototype.open = function() {
    // custom stuff
    return _XMLHttpRequest.prototype.open.apply(this, arguments);
}

Method 3: Full proxy to nati开发者_运维技巧ve XMLHttpRequest

var _XMLHttpRequest = XMLHttpRequest;
XMLHttpRequest = function() {
    this.xhr = new _XMLHttpRequest();
}

// proxy ALL methods/properties
XMLHttpRequest.prototype.open = function() {
    // custom stuff
    return this.xhr.open.apply(this.xhr, arguments);
}

Depending on the JS engine, method 1 produces considerable overhead, since xhr.open is redefined whenever XHR is instantiated.

Method 2 makes me think "why would you need the new _XMLHttpRequest in the first place"? There's a minor feeling of undesired side effects, but it appears to work just fine.

Method 3: simple, old-school, but it won't work straight-away. (Think about reading properties)

In general, I'm personally reluctant when it comes to overwriting browser objects, so that would be a big con to all three methods. Better use some other variable like ProxyXHR (just my 2 cents)

It may depend on the use case. In my case I wanted to create a complete proxy which seems to be only possible with the third method. The problem is that onreadystatechange needs to be set on the original XHR implementation. I guess there are getter and setter defined that cannot be changed from outside.

Because of this method 1 and 2 will not work. To achieve this I wrote a complete, meaning I didn't find any bugs, proxy to XHR here: A: How can I catch and process the data from the XHR responses using casperjs?. It needs to be done with method 3.

I have tried all 3. I have to intercept calls from within code that I do not manage that already has Boomerang AutoXHR plugin running and intercepting calls. #2 and #3 just resulted in errors but #1 worked perfectly in my strange messed up use-case.

Use the below config

_XMLHTTPRequest.setProxy(proxySetting, varProxyServer, varBypassList);

Parameters Details: proxySetting - proxy configuration ex: SXH_PROXY_SET_DEFAULT, SXH_PROXY_SET_DIRECT, SXH_PROXY_SET_PROXY, SXH_PROXY_SET_PRECONFIG

varProxyServer - The name of a proxy server

varBypassList - host names or IP addresses for which you want to permit bypass of the proxy server.