title: What does the comma operator do in JavaScript?
body: <p>If I use:</p>
  
  <pre><code>1.09 * 1; // returns "1.09"
  </code></pre>
  
  <p>But if I use:</p>
  
  <pre><code>1,09 * 1; // returns "9"
  </code></pre>
  
  <p>I know that 1,09 isn't a number.</p>
  
  <p>What does the comma do in the last piece of code?</p>
  
  <h2>More Examples</h2>
  
  <pre><code>if (0,9) alert("ok"); // alert
  if (9,0) alert("ok"); // don't alert
  </code></pre>
  
  <hr>
  
  <pre><code>alert(1); alert(2); alert(3); // 3 alerts
  alert(1), alert(2), alert(3); // 3 alerts too
  </code></pre>
  
  <hr>
  
  <pre><code>alert("2",
      foo = function (param) {
          alert(param)
      },
      foo('1')
  )
  foo('3'); // alerts 1, 2 and 3
  </code></pre>