// 选择<p>JavaScript</p>:

var js = document.querySelector('#test-p');

// 选择<p>Python</p>,<p>Ruby</p>,<p>Swift</p>:

var arr = document.getElementsByClassName('c-red c-green')[0].getElementsByTagName('p');

// 选择<p>Haskell</p>:

var haskell = document.getElementsByClassName('c-green')[1].lastElementChild;