Uncaught ReferenceError: year is not defined in google chart using ajax/codeigniter - ajax

Question

Good day. I want to make my column char working with database but I got this error says "Uncaught ReferenceError: year is not defined". here is my code.
JAVASCRIPT
function year()
{
var e = document.getElementById("selectyear");
var year = e.options[e.selectedIndex].text;
//Ajax Load data from ajax
$.ajax({
url : "<?php echo site_url('chartcontroller/chart/')?>/" + year,
type: "GET",
dataType: "JSON",
success: function(data)
{
drawChart1(data);
},
error: function (jqXHR, textStatus, errorThrown)
{
alert('Error get data from ajax');
}
});
}
google.load("visualization", "1", {packages:["corechart"]});
google.setOnLoadCallback(drawChart1);
function drawChart1(data) {
var data = google.visualization.arrayToDataTable([
['Courses', 'S.Y. 2011-2012', 'S.Y. 2012-2013','S.Y. 2013-2014'],
for(var i = 1; i < data.length; i++) {
comment = data[i];
[comment.Course, comment.year_a, comment.year_b, comment.year_c],
}
]);
var options = {
title: 'ColumnChart',
hAxis: {title: 'Courses', titleTextStyle: {color: 'blue'}}
};
var chart = new google.visualization.ColumnChart(document.getElementById('chart_div1'));
chart.draw(data, options);
}
//ajax end
and my view html
<div class="grid text-center" style="display: block;">
<h1 style=" color: black; font-size: 18px;">Summary of Daily Utilization of Library Holdings per Department</h1>
<div class="input-group">
<span class="input-group-addon">#</span>
<select id="selectyear" class="form-control selectyear" data-mobile="true" name="year" onchange="year();">
<?php
for ($i=$min_year; $i <= $max_year; $i++) {
echo "<option>".$i."</option>";
}
?>
</select>
</div>
<h1 style=" color: gray; font-size: 14px;">S. Y. 2011-2012, 2012-2013 & 2013-2014</h1>
<div id="chart_div1" class="chart" style="height: 400px; width: 100%;"></div>
<div id="chart_div2" class="chart" style="height: 400px; width: 100%;"></div>
in my controller
public function chart($year)
{
$data = $this->views->chart($year);
//Either you can print value or you can send value to database
echo json_encode($data);
}
no problem with ajax because when I do a debugging ajax successfully retrieve the value from database, the problem is when I put that value to my column chart like what I did in my code I've got that error.. help me please. this is the last problem I have to my thesis project.. thanks. I want to change the column chart value if the drop down has change.