JSFiddle - React, Tailwind, and code Playground

by redler

HTML

<ul id="foo">
    <li data-characterid="abc">ABC</li>
    <li data-characterid="def">DEF</li>
    <li data-characterid="ghi">GHI</li>
    <li data-characterid="jkl">JKL</li>
</ul>

JavaScript

function isDupe(which) {
    var result = false;
    $('ul#foo li').each(function(i, e) {
        if ( $(e).data('characterid') == which ) {
            result = true;
            return false; // break out of .each()
        }
    });
    return result;
}

alert(isDupe('abc'));
alert(isDupe('bcd'));