getElementsByClassNameの代替関数

gistfile1.js

function AdaptiveGetElementsByClassName(clazz) {
  var elems = this.getElementsByTagName('*'),
    evClass = ' '+clazz+' ',
          i = 0,
          e = null,
         rv = [];

  while ( e = elems[i] ) {
    if ( e.nodeType === Node.ELEMENT_NODE && (' '+e.className+' ').indexOf(evClass) !== -1 ) {
      rv.push(e);
    }
    i++;
  }
  rv.item = function(i) {
    return this[i];
  };
  return rv;
}