If you don't debug the function using console.log, it throws an unexpected error. But as soon as you want to debug it, it works like a charm (I recently had an occurence like this, and instead of fixing the bug, I needed to create this gist as a joke). "Works" for every global function you create in the browser. Just copy and paste this code int…

schroedinger.js

function notFunny() {
 function s(fn = () => {}) {
    return () => {
      const fnStr = fn.toString();
      console.log(fnStr);
      const keywords = ['console', 'debugger'];
      if (!keywords.find(key => fnStr.includes(key)))
          throw new Error(`Uncaught ReferenceError: ${fn.toString().slice(0, 10)} is not defined`);
      fn();
    }
  }

  for (let obj in window) {
    if (typeof window[obj] === 'function')
      window[obj] = s(window[obj]);
  } 
}

window.setInterval(notFunny, 300);
notFunny();

o.O