Get the keyboard button pressed during onClick and based on that run different functions

When you bind a function to onclick in the HTML tag you want to just pass the name of the function as the event parameter will be passed in by the DOM

<button type="button" id="b41" onclick="myFunction()">myButtonName</button>

but also, a button's click event won't have any keyboard data attached to it, so you may want to look into using keydown and keyup event listeners (probably on the window object) to keep track of which keys are pressed and using that information when the button is clicked

<button type="button" id="b41" onclick="myFunction()">myButtonName</button>
<span id="output"></span>

<script>
  const pressedButtons = {};

  const outputSpan = document.querySelector('#output');

  window.onkeydown = (e) => (pressedButtons[e.which] = true);
  window.onkeyup = (e) => (pressedButtons[e.which] = false);

  function myFunction(event) {
    console.log(pressedButtons);
    if (pressedButtons[97]) {
      outputSpan.innerHTML = 'numpad 1';
    } else if (pressedButtons[98]) {
      outputSpan.innerHTML = 'numpad 2';
    } else {
      outputSpan.innerHTML = '';
    }
  }
</script>

Edit: updated to change text of a span rather than use alert()