How to use a very efficient for loop statement_javascript skills

Add styles to each row of the table. Pay attention to the second parameter of for. When the array subscript is out of bounds, row=row[i] returns false, and the loop ends.

var rows = document.getElementsByTagName('tr');
for( var i = 0, row; row = rows[i]; i ) {
row.className = 'newclass' ;
}
Test code:

nbsp;html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

li { margin-left:28px;}
.abc {background-color:#eee;font-size:14px; margin-bottom:10px;}

<script> <BR><!-- <BR>function a(){ <BR> var row = document.getElementsByTagName("li"); <BR> var t1 = new Date(); <BR> for (var i=0,j; j=row[i]; i++) <BR> { <BR> j.className="abc"; <BR> } <BR> var t2 = new Date(); <BR> alert("耗时 "+(t2-t1).toString()+" 毫秒"); <BR>} <BR>function b(){ <BR> var row = document.getElementsByTagName("li"); <BR> var t1 = new Date(); <BR> for (var i=0; i<row.length; i++) <BR> { <BR> row[i].className="abc"; <BR> } <BR> var t2 = new Date(); <BR> alert("耗时 "+(t2-t1).toString()+" 毫秒"); <BR>} <BR>function c(){ <BR> var j="<ol>"; <BR> for (var i=0; i<2000; i++) <BR> { <BR> j=j+"<li>测试文字"; <BR> } <BR> j=j+""; <BR> document.getElementById("box").innerHTML = j; <BR>} <BR>//--> <BR></script>