height-script.js

async function setElevation(value) {
  // Scenarios:
  //   - Tokens are selected, hovered token is undefined.
  //       - Set elevation of selected tokens.
  //   - Tokens are selected, hovered token is in selection.
  //       - Set elevation of selected tokens.
  //   - Tokens are selected, hovered token is not in selection.
  //       - Set elevation of hovered token.
  //   - No tokens are selected, hovered token is undefined.
  //       - Do nothing
  //   - No tokens are selected, hovered token is defined.
  //       - Set elevation of hovered token.
  const selectedTokensMap   = canvas.tokens._controlled;
  const selectedTokensArray = canvas.tokens.controlled;
  const hoveredToken        = canvas.tokens._hover;

  let tokens = undefined;
  if (hoveredToken == undefined || hoveredToken._id in selectedTokensMap){
    tokens = selectedTokensArray;  
  } else {
    tokens = [hoveredToken];
  }

  let updates = tokens.map(
    token => {
      _id: token.id,
      elevation: (value === 0 ? 0 : token.data.elevation + value)
    }
  );

  await canvas.scene.updateEmbeddedDocuments("Token", updates);
};


Hooks.on("init", () => {
  for (const i of [-10, -5, 0, +5, +10]) {
    const description = (i == 0) ? `Reset token elevation to ${i}` : `Change token elevation by ${i}`;
    game.keybindings.register("pf2e-f-is-for-flatfooted", `elevation${i}`, {
      name: description,
      editable: [],
      onDown: () => {
        setElevation(i);
      }
    })
  }
});


Hooks.on("renderTokenHUD", function(html){
  const elevationElement = html.find('.elevation');

  html.bind('wheel', function(e){
    const heightDelta = 5 * Math.sign(e.originalEvent.wheelDelta); 
    setElevation(heightDelta);
  });
})