PreventDefault on Blazor input

I have a simple application with an input field that should insert a predefined piece of text as you type.

The code I have looks like this:

<input type="text" bind="@PetitionInput" onkeydown="@PetitionHandleKeyDown" />@functions{    private int _petitionCharStep = 0;    private string _petition = "This is a dummy text";    public string PetitionInput { get; set; } = string.Empty;    void PetitionHandleKeyDown(UIKeyboardEventArgs arg) {        PetitionInput += _petition[_petitionCharStep];        _petitionCharStep++;        Console.WriteLine(PetitionInput);    }}

When the input field has focus, and I press a letter on my keyboard, then it should add the first letter from the string _petition to the input. When I press any letter on my keyboard, it should enter the second letter into the input field. And so on.

The problem I have is that it also adds the letter at the end of the input that I pressed on my keyboard. I want to prevent that from happening.

Is there a way to fix this using issue Blazor code only?

I have an online demo here.