Beginner Question: Using Open Method Does Not Load My Text File

server: apache http server 2.2 problem: code does not load my text file hello people. im currently trying to learn javascript and am following several tutorials. written below is a

Solution 1:

In myFunction the xmlhttp variable is not in the scope of the function. This should be causing a JavaScript error, which you can view in Chrome by going to Menu > Tools > JavaScript console. One way to fix this would be to pass the xmlhttp object as a parameter.

functionloadXMLDoc(url , cfunc) {
    //some code...
    xmlhttp.onreadystatechange=function() {
        //pass xmlhttp as a parameter to this function and preserve the context//see https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/call
        cfunc.call(this, xmlhttp);
    }
    //some more code...
}

functionmyFunction() {
    loadXMLDoc("ajax_info.txt", function(xmlhttp) {
        //xmlhttp is now in scope because we passed it as a parameter
    });
}

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Update

I created a working example at http://jsfiddle.net/6rPgE/

As for your question about the modifications I suggested... The second parameter to the loadXMLDoc method (cfunc) is a function. In this case, an anonymous function is created inside myFunction which will be passed as the cfunc parameter to loadXMLDoc. When the onreadystatechange callback is invoked, the cfunc function is called with xmlhttp as the first parameter. This parameter is passed into the anonymous function defined inside myFunction, and is responsible for actually doing something with the AJAX response. On an entirely different note, I highly recommend using a debugger (Chrome has one built-in) and the information provided by the browser's error console to assist you in debugging these issues in the future. Learning how to use a debugger will save you countless hours of banging your head against the wall.

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Update 2

Just thought it would be nice to look at how this can be done using jQuery with quite a bit less code. AJAX is one area where it can be really nice to use a library that abstracts away the details.

Another example that uses jQuery at http://jsfiddle.net/j9QvE/1/

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Update 3

Note that in my code I replaced the path to ajax_info.txt with a path specifically used for testing AJAX functionality in jsFiddle (/echo/js/?js=Success!). This was necessary because ajax_info.txt does not exist on the jsFiddle servers, so requesting it would have resulted in a 404 error. Don't forget to change the path to point to an appropriate resource on your own domain.