js，其中一行代码不懂其作用

Question

html控制div属性#outer{width:500px;margin:0auto;padding:0;text-align:center;}#div1{width:100px;height:100px;background:black;margin:10pxauto;display:block;}varchangeStyle=function(elem,attr,value){elem.style[attr]=value};window.onload=function(){varoBtn=document.getElementsByTagName("input");varoDiv=document.getElementById("div1");varoAtt=["width","height","background","display","display"];varoVal=["200px","200px","red","none","block"];for(vari=0;i