js动态切换背景图片会闪烁

setTimeout(function () {  
   
   document.body.style = 'background-image: linear-gradient(to bottom, rgba(0,0,0,0.5), rgba(0,0,0,0.5)), url("resource/images/dms3/u1.jpg")'; 

 }, 2500);  

setTimeout(function () {
   document.body.style = 'background-image: linear-gradient(to bottom, rgba(0,0,0,0.4), rgba(0,0,0,0.4)), url("resource/images/dms3/u1.jpg")';
 }, 3500);    

 setTimeout(function () {
   document.body.style = 'background-image: linear-gradient(to bottom, rgba(0,0,0,0.3), rgba(0,0,0,0.3)), url("resource/images/dms3/u1.jpg")';
 }, 4500);