JavaScript Self Invoking Function on addEventListener

I'm not being able to make a function of an Event Listener self invoke and the listener to work.

The following code executes the function, but the Event Listener don't work:

window.addEventListener("resize", (function () {
document.getElementById("divMenu").innerHTML = document.getElementById("divTop").offsetWidth
})())

The function will set a needed (dynamic since the beginning) CSS style essential to the website formatting. The "resize" function MUST be executed at load. Is it possible to make this, or should i create a separate Self Invoking Function and call it on the Event Listener?

When you immediately invoke the function, it's return value is put in it's place (window.addEventListener('resize', undefined)). Instead, define your function outside of the event listener then add it and call it.

function onResize() {
  document.getElementById('divMenu').innerHTML = document.getElementById("divTop").offsetWidth;
}
window.addEventListener('resize', onResize);
onResize();

Technically, you could make this work using a self-invoking function but it's a bit screwy and I wouldn't suggest it.

window.addEventListener('resize', (function onResize() {
  document.getElementById('divMenu').innerHTML = document.getElementById("divTop").offsetWidth;
  // Works because it returns a function
  return onResize;
})());