I personally love both JavaScript and Python. For this reason, from time to time I like to port functions that are available in Python, over to JavaScript. The following is a port of the expandTabs function.

String.prototype.expandTabs = function(tabSize) {
  tabSize = Math.min(Math.max(parseInt(+tabSize || 8), 1), 32);
  return this.replace(/^.*\t.*$/gm, function(line) {
    var allBefore = "";
    return line.replace(/(.*?)(\t+)/g, function(match, before, tabs) {
      allBefore += before;
      tabs = new Array(1 + tabSize * tabs.length - allBefore.length % tabSize).join(" ");
      allBefore += tabs;
      return before + tabs;
    });
  });
};

The biggest difference between this JavaScript version and the Python version is the limitation of a 32 character tab size. If you want to increase the maximum tab size, simply change 32 to something else.