function getSource(fn, altSource) {
    var result = altSource;
    if (isStringable(fn)) {
      result = String(fn);
    } else if (has.decompilation) {
      result = (/^[^{]+{([\s\S]*)}\s*$/.exec(fn) || 0)[1];
    }
    return (result || '').replace(/^\s+|\s+$/g, '');
  }
Gets the source code of a function.
@private
@param {Function} fn The function.
@param {String} altSource A string used when a function's source code is unretrievable.
@returns {String} The function's source code.