document.getElementsByClassName的实现

取自Prototype.js框架。

document.getElementsByClassName = function(className, parentElement) {
  if (Prototype.BrowserFeatures.XPath) {
    var q = ".//*[contains(concat(' ', @class, ' '), ' " + className + " ')]";
    return document._getElementsByXPath(q, parentElement);
  } else {
    var children = ($(parentElement) || document.body).getElementsByTagName('*');
    var elements = [], child;
    for (var i = 0, length = children.length; i < length; i++) {
      child = children[i];
      if (Element.hasClassName(child, className))
        elements.push(Element.extend(child));
    }
    return elements;
  }
};