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<html lang="en">
<head>
    <meta charset="utf-8"/>
    <title>Shared Preferences</title>
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    <link rel="stylesheet" href="css/shared-preferences.css">
    <link href="https://fonts.googleapis.com/css?family=Josefin+Sans:400,700" rel="stylesheet">

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        function httpPost(url, body, successCallback, errorCallback) {
            url = '/' + url;

            let xhr 