找了好多，都是由100到0就结束了，到头来自己魔改，以下就是源码。
div中加入img，js添加函数，完事（调用），取名后面加个1是为了避免冲突
1 <!DOCTYPE HTML> 2 <html> 3 <head> 4 <meta charset="utf-8" /> 5 <title>简单透明度渐变</title> 6 </head> 7 8 <body> 9 <div id="img_eat" style="opacity:1;"> 10 <img src="https://images.cnblogs.com/cnblogs_com/ikaros-521/1529977/o_eat.gif" id="eat" alt="" style=" 100px;"/> 11 </div> 12 </body> 13 <script type="text/javascript"> 14 window.onload = function(){ 15 // 透明度来回变换 16 var timer1 = setInterval(colorLiner,20); 17 var val1 = 100; 18 function colorLiner(){ 19 var Div = document.getElementById('img_eat'); 20 if(val1 >= 0) 21 { 22 Div.style.opacity = val1/100; 23 } 24 if(val1 < 0) 25 { 26 Div.style.opacity = -val1/100; 27 } 28 if(val1 == -100)//由-100变为正100 29 { 30 val1 = -val1; 31 } 32 val1--; 33 } 34 } 35 </script> 36 </html>