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• JavaScript
• HTML
• Result

$('li').html(function(i){
    return 'my index is - ' + i;
});

<ul id="foo">
    <li class="other">Beef Jerky</li>
    <li>Smoked Salmon</li>
    <li class="other">Rocky Mountain Oysters</li>
    <li class="other">Beef Jerky</li>
    <li>Smoked Salmon</li>
    <li class="other">Rocky Mountain Oysters</li>
</ul>