<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
.box{
width: 200px;
height: 200px;
background-color: #3295F2;
}
</style>
</head>
<body>
<div class="box" id="box" tabindex="1"></div>
<script>
document.getElementById('box').onblur = function(){
alert('div blur');
};
</script>
</body>
</html>