MAX_IMG_NUMBER = 7 ASSET_PATH = "\"assets/frame1/" ASSET_SUFFIX = ".JPG\"" var frames = [ { DOMElement : "", IMGCounter : 0, }, { DOMElement : "", IMGCounter : 0, }, { DOMElement : "", IMGCounter : 0, } ] FOOBAR = "" document.addEventListener('DOMContentLoaded', function() { frames[0].DOMElement = document.querySelector("#left.side .frame") frames[1].DOMElement = document.querySelector("#right.side .frame") frames.forEach(function(val, i) { if (frames[i].DOMElement != "") { nextImage(frames[i]) } }); }, false); document.addEventListener("keypress", function(keyEvent) { switch (keyEvent.key) { case "q": targetFrame = frames[0] prevImage(targetFrame) break; case "w": targetFrame = frames[0] nextImage(targetFrame) break; case "a": targetFrame = frames[1] prevImage(targetFrame) break; case "s": targetFrame = frames[1] nextImage(targetFrame) break; case "y": targetFrame = frames[2] prevImage(targetFrame) break; case "x": targetFrame = frames[2] nextImage(targetFrame) break; } }, false); function nextImage(targetFrame) { console.log(targetFrame) if (targetFrame.IMGCounter >= MAX_IMG_NUMBER) { targetFrame.IMGCounter = 0 } else { targetFrame.IMGCounter++ } setFrameImage(targetFrame.DOMElement, ASSET_PATH + targetFrame.IMGCounter + ASSET_SUFFIX) } function prevImage(targetFrame) { if (targetFrame.IMGCounter <= 0) { targetFrame.IMGCounter = MAX_IMG_NUMBER } else { targetFrame.IMGCounter-- } setFrameImage(targetFrame.DOMElement, ASSET_PATH + targetFrame.IMGCounter + ASSET_SUFFIX) } function setFrameImage(frame, imgPath) { frame.style.backgroundImage = "url(" + imgPath + ")" }