// JavaScript Document

//pagetop Scroll

function backToTop() {
    var x1 = x2 = x3 = 0;
    var y1 = y2 = y3 = 0;

    if (document.documentElement) {
        x1 = document.documentElement.scrollLeft || 0;
        y1 = document.documentElement.scrollTop || 0;
    }

    if (document.body) {
        x2 = document.body.scrollLeft || 0;
        y2 = document.body.scrollTop || 0;
    }

    x3 = window.scrollX || 0;
    y3 = window.scrollY || 0;

    var x = Math.max(x1, Math.max(x2, x3));
    var y = Math.max(y1, Math.max(y2, y3));

    window.scrollTo(Math.floor(x / 2), Math.floor(y / 2));

    if (x > 0 || y > 0) {
        window.setTimeout("backToTop()", 25);
    }
}


// Scroll Smooth
function SmoothScroll(targetID){
  if( !document.getElementById ) {return true;}
  var step=30;  //初速度
  var max=200;  //最高速度
  var accel=5;  //加速度
  var interval=30;  //加速インターバル
  var current_y = document.body.scrollTop;
  var element=document.getElementById(targetID);
  if (!element){return true;}
  var target_y = 0;
  for (i = element;i.offsetParent;i=i.offsetParent ){
    target_y += i.offsetTop;
  }
  var count=0;
  if ( current_y > target_y ){ step = -(step); accel = -(accel);}
  var timerid = setInterval(function(){
    if (step<max) step += (count*accel);
    if ( Math.abs(current_y-target_y) < Math.abs(step) ){
      window.scrollTo(document.body.scrollLeft,target_y);
      clearInterval(timerid);
      return false;
    }else{
      window.scrollBy(0,step);
      current_y += step;
      count++;
    }
  },interval);
  return false;
}