<div class="checkoutDiv" style=" display:flex;">
	<input type="text" name="ean" id="focus" placeholder="Баркод" style="width: 250px; margin:10px;" autocomplete="off" autofocus>
	<input type="text" name="num" value="1" style="width: 50px; margin:0; text-align: center;">
	</div>

	<div class="checkoutDiv" style="display: none;">
	<input type="text" name="ean" placeholder="Баркод" style="width: 250px; margin:10px;" autocomplete="off" autofocus>
	<input type="text" name="num" value="1" style="width: 50px; margin:0; text-align: center;">
	</div>

	<div class="checkoutDiv" style="display: none;">
	<input type="text" name="ean" placeholder="Баркод" style="width: 250px; margin:10px;" autocomplete="off" autofocus>
	<input type="text" name="num" value="1" style="width: 50px; margin:0; text-align: center;">
	</div>


	<script>
	function callback(e){
    if (
        $(this).index() == $('#checkout div[display="flex"]').length - 1
            &&
        e.which == 13
    ) {
        $(this).next('div[display="none"]').prop("display", "flex").keypress(callback)
    	}
	}

	$('#checkout div[display="none"]').keypress(callback)
</script