JSFiddle - React, Tailwind, and code Playground

JavaScript

function min(collection, callback) {
    if (collection.length == 0) {
        return null;
    }
    
    var minIndex = 0;
    var minValue = callback(collection[0]);
    for (var i = 1; i < collection.length; ++i) {
        if (minValue > callback(collection[i])) {
            minValue = callback(collection[i]);
            minIndex = i;
        }
    }
    
    return collection[minIndex];
}

var items = [ "John/20", "Mary/18" ];

var minItem = min(items, function(item) {
    return item.split('/')[1]; // get the "age" part
});

alert(minItem);