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<!DOCTYPE html>
<html>
<head>
<title>JS tutorial</title>
<style type="text/css">
body {
    margin-top:20px;
    background-color:#bfb;
}
</style>
<script type="text/javascript">
    var val1 = null;
    var val2 = false;
    var val3 = true;
    document.write("The result of <i>( !"+val1+" )</i> is: <br /><b>" + (!val1) + "</b><br /><br />");
    document.write("The result of <i>( !!"+val1+" )</i> is: <br /><b>" + (!!val1) + "</b><br /><br />");
    document.write("The result of <i>( "+val2+" && "+val3+" )</i> is: <br /><b>" + (val3 && val2) + "</b><br /><br />");
    document.write("The result of <i>( "+val1+" || "+val3+" )</i> is: <br /><b>" + (val1 || val3) + "</b>");
</script>   
​
</head>
<body>
​
</body>
</html>