echart issue with connect - html

<!DOCTYPE html>
<html>
<head>
</head>
<body>
    <div>
        <div class="graph graph1" id="graph1" style="width: 500px; height: 300px;"></div>
        <div class="graph graph2" id="graph2" style="width: 500px; height: 300px;"></div>
        <div class="graph graph3" id="graph3" style="width: 500px; height: 300px;"></div>
    </div>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/echarts/4.2.1/echarts.min.js"></script>
<script type="text/javascript" src="./script.js"></script>
</body>