Test Case Boilerplate

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HTML

<div id="d1">
    <p id="p1">blah!</p>
</div>
<div id="d2" style='display:none;'>
    <p id="p2">blah!</p>
</div>

JavaScript

//this problem doesn't occur in JSFiddle.

console.log($("#d1").height());
console.log($("#p1").height());

//invisible
console.log($("#d2").height());
console.log($("#p2").height());