var fn=setInterval(function(){},1000)
每隔1秒执行一次函数
clearInterval(fn)
清除计时器
判断当图片放大缩小到固定大小时，清除计时器
完整代码
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>demo</title> <style> body,h1,h2,h3,h4,h5,h6,hr,p,blockquote,dl,dt,dd,ul,ol,li,pre,form,fieldset,legend,button,input,textarea,th,td{margin:0;padding:0;} body,button,input,select,textarea{font:12px/1.5 tahoma,arial,\5b8b\4f53;} h1,h2,h3,h4,h5,h6{font-size:100%;} address,cite,dfn,em,var{font-style:normal;} code,kbd,pre,samp{font-family:courier new,courier,monospace;} small{font-size:12px;} ul,ol{list-style:none;} a{text-decoration:none;} a:hover{text-decoration:underline;} sup{vertical-align:text-top;} sub{vertical-align:text-bottom;} legend{color:#000;} fieldset,img{border:0;} button,input,select,textarea{font-size:100%;} table{border-collapse:collapse;border-spacing:0;} .clear{clear: both;float: none;height: 0;overflow: hidden;} </style> </head> <body> <div> <img src="https://img.mukewang.com/53577ee900016c2102080260.jpg" /><br> <input type="button" value="放大" /> <input type="button" value="缩小" /> </div> <script type="text/javascript"> function pic_max(){ var maxBtn=document.getElementById("max"); var minBtn=document.getElementById("min"); maxBtn.onclick=function(){ max(); } var img=document.getElementById("myImage"); var maxHeight=img.height*2; var maxWidth=img.width*2; function max(){ var endHeight=img.height*1.3; var endWidth=img.width*1.3; var maxTime=setInterval(function(){ if(img.height<endHeight&&img.width<endWidth){ if(img.height<maxHeight&&img.width<maxWidth){ img.height=img.height*1.05; img.width=img.width*1.05; }else{ alert("图片已经是最大值了") clearInterval(maxTime); } }else{ clearInterval(maxTime); } },20); } minBtn.onclick=function(){ min(); } var img=document.getElementById("myImage"); var minHeight=img.height*0.5; var minWidth=img.width*0.5; function min(){ var overHeight=img.height*0.7; var overWidth=img.width*0.7; var minTime=setInterval(function(){ if(img.height>overHeight&&img.width>overWidth){ if(img.height>minHeight&&img.width>minWidth){ img.height=img.height*0.95; img.width=img.width*0.95; }else{ alert("图片已经是最小值了") clearInterval(minTime); } }else{ clearInterval(minTime); } },20); } } window.onload=function(){ pic_max(); } </script> </body> </html>