Get paragraph text inside an element
===

I want to have the text value from a    <p> inside a    <li> element. 
html:
    <ul>
      <li onclick="myfunction()">
        <span></span>
        <p>This Text</p>
      </li>
    </ul>

javascript:
    function myfunction() {
      var TextInsideLi = [the result of this has to be the text inside the paragraph"];
    }

How to do this?