Explain this query

Question

Hi,

 

    Can anyone  explain this query?

 

 

<script>

$(function() {

var pgurl = window.location.href.substr(window.location.href.lastIndexOf("/") +1);

$(".menu li a").each(function() {

if ($(this).attr("href") == pgurl   || $(this).attr("href") == '')

$(this).addClass("active");

});

});

</script>

 

 and why we add  '1' in 3rd line (highlight with red color)?

 

 Thanks in advance.