JSFiddle - React, Tailwind, and code Playground

JavaScript

function () {
    function each(array, fn) {
        for (var i = 0; i < array.length; ++i) {
            fn(array[i], i);
        }
    };
    each(['a', 'b', 'c'], function (letter, index) {
        console.log(index + ': ' + letter);
    });
};

(function () {
    function each(array, fn) {
        for (var i = 0; i < array.length; ++i) {
            fn(i, array[i]);
        }
    };
    each(['a', 'b', 'c'], function (index, letter) {
        console.log(index + ': ' + letter);
    });
}());