how to import jquery in js file

JavaScript
<head>

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>

</head>
 var script = document.createElement('script');
script.src = 'https://code.jquery.com/jquery-3.4.1.min.js';
script.type = 'text/javascript';
document.getElementsByTagName('head')[0].appendChild(script);
Source

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