ASP.NET Core Blazor VirtualList

_Host.cshtml

<!-- To be added to _Host.cshtml -->
<script>
    window.blazorHelpers = {
        getScrollTop : function (element) {
            return element.scrollTop;
        },
        setScrollTop : function (element, value) {
            element.scrollTop = value;
            return element.scrollTop;
        }
    }
</script>

VirtualList.razor

@typeparam TItem
@inject IJSRuntime JSRuntime

<div @ref="scrollContainer" @ref:suppressField style="height: 300px; position: relative; overflow: auto;" @onscroll="HandleScroll">
    <div style="height: @(rowHeight*Items.Count())px; width: 1px; position: absolute; top: 0; left: 0;"></div>

    @foreach (var virtualRow in VirtualRows)
    {
        <div style="height: 150px; width: 30px; background-color: gray; position: absolute; top: @(virtualRow.Top)px; left: 0;">@RowTemplate(virtualRow.Item)</div>
    }
</div>

<p>@x scrollTop: @currentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

@code {
    class VirtualRow
    {
        int rowHeight = 150;
        public TItem Item { get; set; }
        public int Index { get; set; }
        public int Top => Index * rowHeight;
    }

    IList<VirtualRow> VirtualRows = new List<VirtualRow>();

    [Parameter]
    public RenderFragment<TItem> RowTemplate { get; set; }

    [Parameter]
    public IList<TItem> Items { get; set; }

    ElementReference scrollContainer;
    int currentCount = 0;
    int virtualRowCount = 10;
    int virtualRowOffset = 0;
    int rowHeight = 150;

    protected override void OnParametersSet()
    {
        for (int i = 0; i < virtualRowCount; i++)
        {
            VirtualRows.Add(new VirtualRow {Item = Items[i], Index = i});
        }
    }

    async Task IncrementCount()
    {
        currentCount+=10;
        await JSRuntime.InvokeAsync<int>("blazorHelpers.setScrollTop", scrollContainer, currentCount);
    }

    async Task HandleScroll(UIEventArgs args)
    {
        var scrollTop = await JSRuntime.InvokeAsync<int>("blazorHelpers.getScrollTop", scrollContainer);

        currentCount = scrollTop;

        if (VirtualRows.First().Top < scrollTop)
        {
            virtualRowOffset++;
            for (int i = 0; i < VirtualRows.Count() - 1; i++)
            {
                VirtualRows[i] = VirtualRows[i+1];
            }
            int j = VirtualRows.Count() - 1;
            int itemsOffset = virtualRowOffset + j;
            VirtualRows[j] = new VirtualRow {Item = Items[itemsOffset], Index = itemsOffset};
        }
    }
}