iframe.js

// Function to send the size of the page to the parent
const sendSize = function () {
  const message = {
    iframeResize: {
      height: document.body.scrollHeight,
      width: document.body.scrollWidth
    }
  };
  window.top.postMessage(message, "*");
};

// Function to send the redirect trigger to the parent
const questionnaireRedirect = function () {
  const message = { iframeRedirect: true };
  window.top.postMessage(message, "*");
};

window.addEventListener("resize", sendSize, false);
window.addEventListener("load", sendSize, false);

// Can be removed if triggering the redirect function in another way
document
  .getElementById("button")
  .addEventListener("click", questionnaireRedirect, false);