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<title>JavaScript undefined</title>
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<pre> <!-- Use pre element for work document.writeln() method -->
<script type="text/javascript">
var str; // Identify as undefined value.
document.writeln("str == null : ", str == null);
document.writeln("undefined == null : ", undefined == null);
var bool = Boolean(str);
document.writeln("bool : ", bool); // Boolean context Returns false
</script>
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