For when you want to run a function but don't know when it's going to be defined. Keep checking until you WIN!

wait-for-function.js

/* ===================================
* Scenario:
* You want to run a function but don't know when it's going to be defined.
* You keep checking if it's defined every 0.25 seconds. When it's defined, stop checking.
*
* Copyright (c) 2018, Wallace Sidhrée
* MIT License
====================================== */

// On doc ready for modern browsers
document.addEventListener('DOMContentLoaded', (e) => {
  // Scope all logic related to what you want to achieve by using a function
  const waitForMyFunction = () => {
    // Use a timeout id to identify your process and purge it when it's no longer needed
    let timeoutID;
    // Check if your function is defined, in this case by checking its type
    if (typeof myFunction === 'function') {
      // We no longer need to wait, purge the timeout id
      window.clearTimeout(timeoutID);
      // 'myFunction' is defined, invoke it with parameters, if any
      myFunction('param1', 'param2');
    } else {
      // 'myFunction' is undefined, try again in 0.25 secs
      timeoutID = window.setTimeout(waitForMyFunction, 250);
    }
  };
  // Initialize
  waitForMyFunction();
});