How to trigger inline script onload?

I have the following script, as seen, it calls the Date method onClick event, like so:

<!DOCTYPE html>
<html>

<body>

  <p onclick='this.innerHTML = Date();'>click me!</p>


</body>

</html>

How can I do the same with an onLoad event? I don’t want to define it with a separate <script> tag and call it as a function. I’d like the most minimal coding.
Why doesn’t the following work?

<!DOCTYPE html>
<html>

<body>

  <p onload='this.innerHTML = Date();'>date here onload</p>


</body>

</html>