title: How to findIndex with 2 condition?
body: <p>I have 2 arrays.</p>
  <pre><code>    Size = ['Size 0', 'Size 2', 'Size 3']
  
      Cart = ['1', '2', '3'] // 1, 2, 3 = product id
  </code></pre>
  <p>How to get array position with condition <code>size = 'Size 0'</code> and <code>Cart = '2'</code>?</p>
  <p>I tried</p>
  <pre><code>let id = req.params.id; // id = product_id
  let size = req.body.size; 
  k = req.session.size.findIndex(function(a){
              req.session.cart.findIndex(function(c){ 
                  return a == size &amp;&amp; c == id;
      })
  });
  </code></pre>
  <p>but it's not working</p>