title: How to add two strings as if they were numbers?
body: <p>I have two strings which contain only numbers:</p>
  
  <pre><code>var num1 = '20',
      num2 = '30.5';
  </code></pre>
  
  <p>I would have expected that I could add them together, but they are being concatenated instead:</p>
  
  <pre><code>num1 + num2; // = '2030.5'
  </code></pre>
  
  <p>How can I force these strings to be treated as numbers?</p>