Affichage des images aléatoire avec js

<!DOCTYPE html>
<html>
<head>
  <title>RÉCUPÉRER LE NOM DU FICHIER DEPUIS INPUT FILE | par NGLESSON </title>
  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <meta name="author" content="Mezgani said">
  <meta name="copyright" content="NGLESSON">
  <link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet">
  <link href="style.css" rel="stylesheet" type="text/css">
</head>
<body>
  <div class="container">
    <div class="row mx-auto text-centermt-5">
      <div class="col-lg-4 col-12">
        <img src="https://www.nglesson.com/assets/imgs/menu/integration-web.jpg" class="img-fluid" id="attach" alt="attach" title="attach">
      </div>
    </div>
  </div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="script.js"></script>
</body>
</html>
.custom-attach-upload {
    border: 1px solid #999;
    display: inline-block;
    padding: 12px 12px;
    cursor: pointer;
    background: #ccc;
}
.custom-attach-upload:hover {
    background: #FFF;
}
//window.onload = randomImg;

window.onload = function() {
    randomImg();
};

var myFile = new Array("https://www.nglesson.com/assets/imgs/menu/solution-technique.jpg",
"https://www.nglesson.com/assets/imgs/menu/problematique.jpg",
"https://www.nglesson.com/assets/imgs/menu/cours-web.jpg");

function randomImg() {
     var randomNum = Math.floor(Math.random() * myFile.length);
     document.getElementById("attach").src = myFile[randomNum];
}
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