gistfile1.js

function headers(str) {
  var lst = str.split("\n");
  var hdr = {};
  hdr.__proto__ = null;
  lst.forEach(function (x) {
    if (!x.length)
       return;
    [ name, value ] = x.split(/\s*:\s*/, 2);
    if (!hdr[name])
      hdr[name] = value;
    else if (value)
      hdr[name] += ', ' + value;
  });
}