无法从服务器 .txt 文件中获取文件内容

Question

I'm working in dhtml (html5, CSS3, latest JavaScript, and Perl 5.26.3) using an Apache/2.4.39 (Win64) and mod_perl/2.0.10 server on Windows 10. I don't seem to be able to get ajax to work.

I'm trying to 'get' a multi-line file (directory and file name) out of a database location. I'm thinking that the response text will return a string of lines separated by line ends (\\n). I've tried the w3 simplest approach, jquery, and d3. The w3 approach is below.

    var mFn = document.forms[0]['thefdir'].value + 'Measures/all.mea?t=' + Math.random(); // Unique ID bypasses cache.

    var xhttp = new XMLHttpRequest();
    xhttp.open('GET', 'dog.txt', true);
    xhttp.onreadystatechange = function() {
      if (this.readyState == 4 && this.status == 200) {
        fieldName3 = this.responseText;
      }
    };    
    xhttp.send();

Its executed onChange to a field on a form generated by a Perl CGI program. The fieldName3.value would be processed downstream in the JS.

I've tried it with the fully qualified location (mFn) and a relative location (dog.txt) with 1 line in it. Neither worked. I don't know what directory the relative location resolves to. So I put a copy in the server root and the cgi-bin directories. It did not work. Nothing happens and no error information is generated.

Any help will be appreciated. craigt

Answer 1

The data in the console and finally in an alert looks like a multi-line file where each line ends in a CRLF, as verified by Notepad++. This is what the file on the server is.

Apparently, with the asynchronous request, the downstream javascript gets executed before the request from the server completes. When I change it to a synchronous request it worked as hoped in all 5 browsers. So I ether have to 1) be able to make the JS process wait until the onreadystatechange assignment has completed or 2) accept the synchronous execution. I have read several cautions about 2. The file is small, the activity is aperiodic and increasingly infrequent, and the synchronous effect will be very brief. What do you think about 1 or 2.

And thanks for working with me. I apologize for opening this when I did. I could have done a lot more first.