// 画像のロールオーバー

(function() {
  if (!document.getElementsByTagName) return;

  var addEvent, switchImage, init;
  addEvent = function(obj, type, func) {
    if (obj.addEventListener) {
      obj.addEventListener(type, func, false);
    }
    else if (obj.attachEvent) {
      obj.attachEvent('on' + type, func);
    }
  };
  switchImage = function(event) {
    var img = event.target || event.srcElement;
    img.src = (img.src == img.srcOff) ? img.srcOn : img.srcOff;
  };
  init = function() {
    var imgs = document.getElementsByTagName('img');
    var loaded = {}, img;
    for (var i = 0, len = imgs.length; i < len; i++) {
      img = imgs[i];
      if ( !img.src.match(/^(.*_)off(\..*)$/) ) continue;
      img.srcOff = img.src;
      img.srcOn = RegExp.$1 + 'on' + RegExp.$2;
      addEvent(img, 'mouseover', switchImage);
      addEvent(img, 'mouseout', switchImage);
      if (loaded[img.srcOn]) continue;
      loaded[img.srcOn] = true;
      (new Image).src = img.srcOn;
    }
  };

  addEvent(window, 'load', init);
})();


//スワップイメージ
<!--
function MM_preloadImages() { //v3.0
  var d=document; if(d.images){ if(!d.MM_p) d.MM_p=new Array();
    var i,j=d.MM_p.length,a=MM_preloadImages.arguments; for(i=0; i<a.length; i++)
    if (a[i].indexOf("#")!=0){ d.MM_p[j]=new Image; d.MM_p[j++].src=a[i];}}
}

function MM_findObj(n, d) { //v4.01
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
  if(!x && d.getElementById) x=d.getElementById(n); return x;
}

function MM_swapImage() { //v3.0
  var i,j=0,x,a=MM_swapImage.arguments; document.MM_sr=new Array; for(i=0;i<(a.length-2);i+=3)
   if ((x=MM_findObj(a[i]))!=null){document.MM_sr[j++]=x; if(!x.oSrc) x.oSrc=x.src; x.src=a[i+2];}
}

function MM_swapImgRestore() { //v3.0
  var i,x,a=document.MM_sr; for(i=0;a&&i<a.length&&(x=a[i])&&x.oSrc;i++) x.src=x.oSrc;
}
//-->

<!--include用-->
function include(filename, afterfunc) {

  include.seq = (include.seq)? include.seq + 1: 1;

  var id = new Date().getTime() + "-" + include.seq;
  var inc = document.createElement("iframe");

  inc.id = "inc-" + id;
  inc.src = filename;
  inc.style.display = "none";
  document.write("<span id=\"" + id + "\"></span>");
    
  var incfunc = function() {
    
    var s = (function() {
      var suffix = (n = filename.lastIndexOf(".")) >= 0 ? filename.substring(n): "default";
      if (suffix == ".html") return inc.contentWindow.document.body.innerHTML;
      if (suffix == ".txt") return inc.contentWindow.document.body.firstChild.innerHTML;
      if (suffix == "default") return inc.contentWindow.document.body.innerHTML;
    })();

    var span = document.getElementById(id);

    var insertBeforeHTML = function(htmlStr, refNode) {
      if (document.createRange) {
        var range = document.createRange();
        range.setStartBefore(refNode);
        refNode.parentNode.insertBefore(range.createContextualFragment(htmlStr), refNode);
      } else {
        refNode.insertAdjacentHTML('BeforeBegin', htmlStr);
      }
    };

    insertBeforeHTML(s.split("&gt;").join(">").split("&lt;").join("<"), span);
    document.body.removeChild(inc);
    span.parentNode.removeChild(span);
    if (afterfunc) afterfunc();
  };

  if (window.attachEvent) {
    window.attachEvent('onload', 
      function() {
        document.body.appendChild(inc); 
        inc.onreadystatechange = function() { if (this.readyState == "complete") incfunc(); };
      });
  }
  else {
    document.body.appendChild(inc);
    inc.onload = incfunc;
  }
}
<!--/include用-->