Why does Logging onclick event turns out to be undefined in chrome?

    <ul onClick='pop()'>
    <li id="1">1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
   </ul>

    function pop(event) {
    let ul = document.getElementsByTagName('ul')[0];
    console.log(window.event); //Valid mouseEvent
    console.log(event) // Undefined
}

So the question is that why does logging event results to be undefined whereas window.event has a valid value ? Browser - chrome

Here's how to handle the event in an efficient way. You didn't pass any event to pop.

function pop(event) {
  let ul = document.getElementsByTagName('ul')[0];
  console.log(window.event); //Valid mouseEvent
  console.log(event) // Undefined
}

document.getElementById("yourid").addEventListener('click', pop);

<ul id="yourid">
  <li id="1">1</li>
  <li>2</li>
  <li>3</li>
  <li>4</li>
  <li>5</li>
</ul>