[рони]

Kurt_D_Cobain,
можно так попробовать

function handleFiles(files) {
	    document.querySelectorAll("#gallery > div.new").forEach(div => div.classList.remove("new"));
		initializeProgress(files.length)
        for (let i = 0; i < files.length; i++) {
            let div = document.createElement('div');
            div.className = "new";
            document.getElementById('gallery').appendChild(div)
        };
		files = [...files];
		files.forEach(uploadFile)
		files.forEach(previewFile)
		files.forEach(previewName)
		files.forEach(previewSize)
		files.forEach(removeFile);

	}