Clarification of a some code

I have come across a website that appears to use Ajax but does not include any js file except one file called ajax.js which has the following:

function run(c, f, b, a, d) {
    var e = null;
    if (b && f) {
        document.getElementById(b).innerHTML = f
    }
    if (window.XMLHttpRequest) {
        e = new XMLHttpRequest()
    } else {
        if (window.ActiveXObject) {
            e = new ActiveXObject(Microsoft.XMLHTTP)
        }
    }
    e.onreadystatechange = function () {
        if (e.readyState == 4) {
            if (e.status == 200 || e.statusText == "OK") {
                if (b) {
                    document.getElementById(b).innerHTML = e.responseText
                }
                if (a) {
                    setTimeout(a, 0)
                }
            } else {
                console.log("AJAX Error:  " + e.status + " | "开发者_如何学Go + e.statusText);
                if (b && d != 1) {
                    document.getElementById(b).innerHTML = "AJAX Error.  Please try refreshing."
                }
            }
        }
    };
    e.open("GET", c, true);
    e.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
    e.send(null)
}

Like you might have guessed, the way it issues queries inside the page with queries like this:

run('page.php',loadingText,'ajax-test', 'LoadSamples()');

I must admit that this is the first time I've seen a page from which I could not figure how things are being done. I have a few questions:

• Is this Server-Side Ajax or something similar? If not, can someone clarify what exactly is this?
• Why does one use this? Is it for hiding the design details? (which are otherwise revealed in plain text by javascript)
• How difficult would it be to convert my existing application into this design pattern? (maybe a subjective question but any short suggestion will do)

Any suggestions?

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Not sure what you're exactly asking here, but the function given is actually fairly simple. Decoding the variables / parameters:

• e = AJAX request object
• c = Page to send AJAX request to
• f = Loading text to be displayed in specified element b
• b = id of element to display result in
• a = Function to call if ajax request succeeds
• d = boolean - if true, display an error on failure

Exactly why they're using this particular method I can't really say - seeing the complete page that uses this functionality may help.

I don't think it's hiding any design details. It does look a slightly odd way of doing things to me, but as I said above, there may be specific reasons for this in the way the page it's being used in works.

Can you use this code? Certainly.

Should you use this code? The answer to that is: Is it the right tool for the job?

How difficult would it be to convert your existing code to use this method? That depends on your existing code and whether this is the right tool for the job.

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This is just a function that uses the XMLHttpRequest object to perform asynchronous requests for HTML in order to update the existing document.

Its not a pattern per se, its just one of many ways to dynamically update the document.

Its not 'server-side Ajax' (whats that?), its just plain simple ajax used to update the page.
Why you would use it? To avoid to have to refresh the entire page when only a small section needs to be updated. No competent developer would use this to obfuscate. If you can use the same? Sure.. if thats what you need. If you should? Why not - if thats what you need.

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AJAX is just a buzz word for using XMLHttpRequest to load web content asynchronously from the server into your web document.

That function call is a plain XMLHttpRequest call that requests data from page.php (asynchronously without reloading the page) and puts all the response text into document.getElementById(b).innerHTML. Finally it appears to call the LoadSamples() callback, when the response is received.

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What's the problem? It seems to me it is just someone's home rolled ajax update helper function. Many of us have written lots of those through the times.