const flatten = arr => {

    let outputArr = [];

    // Loop through each index of the array
    arr.forEach(item => {

        // If the current item is not an array, push its value immediately.
        if(!Array.isArray(item)){

            outputArr.push(item);

        // If the current item is an array, recurse into it.
        // It's usually better to not use recursion, but in this case,
        // depth is unknown, and recursion makes sense.
        } else {

            // Spread the results of the recursion into the output array.
            outputArr.push(...flatten(item));
        
        }

    });

    return outputArr;

}

// Created for use with Node or other CommonJS
module.exports = flatten;