amazonPlusHatenaLink.user.js

// ==UserScript==
// @name           amazonPlusHatenaLink
// @namespace      d.hatena.ne.jp/sugarbabe335/
// @description    add HatenaAsinLink for amazon page
// @include        http://www.amazon.co.jp/*
// ==/UserScript==

location.href.match(/(product|dp|ASIN)\/(.{10})\/?/i);
var string = "http://d.hatena.ne.jp/asin/"+RegExp.$2;
var node = xpath("//div[@class='buying']/*[last()]");
if(node[2] != undefined){
  var div = document.createElement('span');
  var a = document.createElement('a');
  a.href=string;
  var text = document.createTextNode("はてな");
  a.appendChild(text);
  div.appendChild(a);
  node[2].parentNode.insertBefore(div, node[2]);
}

//http://yamanoue.sakura.ne.jp/blog/coding/68
function xpath(query) {
  var results = document.evaluate(query, document, null, XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE, null);
  var nodes = new Array();
  for(var i=0; i<results.snapshotLength; i++){
    nodes.push(results.snapshotItem(i));
  }
  return nodes;
}