Getting one data attribute using another

See the DIV below. If I store the data=value attribute “?=url=homepage” in a variable, how can I use it to find the corresponding data-target attribute in the same DIV? There would be a lot of different DIVs but they will all have a unique data-target and data-value that go together. I imagine I can use javascript or jquery to accomplish this.

<header>
<div id="nav" title="Homepage" data-target="practice-page-1.php" data-value="?url=homepage">Homepage</div>
</header>