title: Javascript : optional parameters in function
body: <p>Let's say I have this : </p>
  
  <pre class="lang-js prettyprint-override"><code>function concatenate(a, b, c) {
      // Concatenate a, b, and c
  }
  </code></pre>
  
  
  
  <p>How do I handle those calls ? </p>
  
  <pre class="lang-js prettyprint-override"><code>x = concatenate(a)
  
  x = concatenate(a, b)
  
  x = concatenate(a, c)
  </code></pre>
  
  
  
  <p>How can I make my function aware of the parameter I gave to it ? </p>