title: function.toString() in javascript
body: <p>I don't understand how <strong>f.toString</strong> (<em>without calling it</em>) evaluate to returned result of that same function ? </p>
  
  <pre><code>function f(a){
      console.log(a + a);
      f.toString = function(){return a};// this part is       
  //confusing.
      return f;
  };
  
  f(10) // 20
  f(10)(20)// 20 40
  </code></pre>