How to make the source(path) of MathJax.js environment dependent?

How do I specify the following requirement in my html?

When the computer has access to Internet, the source of MathJax.js is https://c328740.ssl.cf1.rackcdn.com/mathjax/latest/MathJax.js;

When it is offline, and the system is Linux, the source is /MathJax/MathJax.js; if the system is Windows, it is /C:/MathJax/MathJax.js. (It would be even better if I can use environment variable in the local path.)

Solution

You can put MathJax in a location relative to your static HTML file:

<script src="https://c328740.ssl.cf1.rackcdn.com/mathjax/latest/MathJax.js"></script>
<script>
if( !window.MathJax ) {
    document.write(
        '<script type="text\/javascript" src="../lib/MathJax.js"><\/script>'
    );
}
</script>

This way your implementation is independent of the OS.

Another option would be to set up the location according to your browser URL:

<script>
var url= location.protocol == 'http:'? 
         "https://c328740.ssl.cf1.rackcdn.com/mathjax/latest/MathJax.js" :
         "../lib/MathJax.js";
document.write(
    '<script type="text\/javascript" src="' + url + '"><\/script>'
);
</script>