<apex:selectList size="1" styleclass="chartBlock">
<apex:selectOptions value="{!dynamiclist}"></apex:selectOptions>
</apex:selectList>
var visualization = new google.visualization.LineChart(document.getElementById('chartBlock'));
var e = document.getElementsByClassName("chartBlock")[0];
var strUser = e.options[e.selectedIndex].value;
var visualization = new google.visualization.LineChart(strUser);
var e = document.getElementsByClassName("chartBlock")[0];
var strUser = e.options[e.selectedIndex].value;