An example of good code structure for Unclass

code-structure.js

// all variables I will use

var photosArray;
var photosArrayCounter;
var $visiblePhoto;

// all functions

var changePhoto = function() {
    if ($(this).hasClass('next') && photosArrayCounter < photosArray.length) {
        photosArrayCounter++;
    }
    else if ($(this).hasClass('prev') && photosArrayCounter > 0) {
        photosArrayCounter--;
    }

    $visiblePhoto.attr('src', photosArray[photosArrayCounter]);
}

// what should happen when the page loads

$(document).ready(function() {
    // declare variables

    photosArray = ['img1.jpg', 'img2.jpg', 'img3.jpg', 'img4.jpg'];
    photosArrayCounter = 0;
    $visiblePhoto = $('.photo');

    // attach event handlers

    $('.next').click(changePhoto);
    $('.prev').click(changePhoto);

    // call any functions that need to run on page load
    // we don't have any
});