componentDidMount() {
 this.changeFixed()
}
//計算高度
changeFixed(){
 //getDOMNode
 const layoutNode = document.querySelectorAll('.page-layout')[0];
 const orderPriceNode = document.querySelectorAll('.test-price')[0];
 window.addEventListener('scroll', function (e) {
  const windowInnerHeight = window.innerHeight;
  const layoutNodeHeight = layoutNode.offsetHeight;
  //滚动超出视野距离
  let scrollTop = window.pageYOffset|| document.documentElement.scrollTop || document.body.scrollTop;
  const distanceBottom = layoutNodeHeight - scrollTop - windowInnerHeight;
  //120的时候吸底
  if(distanceBottom <= 120){
   orderPriceNode.classList.remove('fixed');
  }else{
   orderPriceNode.classList.add('fixed');
  }
 })
}