Native JS write-round plot effect

<script>varPicarr=[                "pic/lb1.jpg",                "pic/lb2.jpg",                "pic/lb3.jpg",                "pic/lb4.jpg"            ]; //global Variable Index controls the number of pictures that are currently located            varindex=0; vartimer; varRadiobtn= Document.getelementsbyclassname ("Tubiao")[0].getelementsbytagname ("span"); function Autochang (index) {varindex=parseint (index); Document.getelementsbyclassname ("content_1")[0].style.backgroundimage="URL ("+picarr[index]+")";  for(varj=0; j<radiobtn.length;j++) {Radiobtn[j].classname=""; } radiobtn[index].classname="actived"; } function Change (index) {setinterval ("Autochang ((index++)%radiobtn.length);", the); }            //page load Successful initial effectChange (index); //Toggle effect When mouse clicks Point               for(varI=0; i<radiobtn.length;i++) {Radiobtn[i].index=i; Radiobtn[i].onclick=function () {clearinterval (timer); Autochang ( This. Index); Index= This. Index; }             }             //Click the left arrowDocument.getelementsbyclassname ("Left_jiantou")[0].onclick=function () {index--; if(index<0) {Index=radiobtn.length-1;             } autochang (index); }             //Click the right arrowDocument.getelementsbyclassname ("Right_jiantou")[0].onclick=function () {index++; if(index>=radiobtn.length) {Index=0;             } autochang (index); }    </script>

Native JS write-round plot effect