JS Prototype get element by class?

I got the following code and I'm trying to make it match on a class instead of on an id:

Html:

    

        [First Title|http://test.com]
        Another line
        [Second Title|http://test.com]
        More text
        [Third Title|http://test.com]
    

Javascript:

var textContainer = document.getElementById("testdiv");
var linkText = textContainer.innerHTML;
var pattern = /\[([^|]+)\|([^>]+.?)[^<]*(<\/a>)\]/g;
var result = linkText.replace(pattern, "$2$1$3");

textContainer.innerHTML = result;

Full example: http://jsfiddle.net/JFC72/17/

How can I make it match on "myclass" instead? Thanks!