title: Javascript calling function expression
body: <p>It makes sense by calling the function this way:</p>
  
  <pre><code>print(square(5));  
  function square(n){return n*n}
  </code></pre>
  
  <p>But why the following calling doesn't work?</p>
  
  <pre><code>print(square(5));  
  square = function (n) {  
    return n * n;  
  }  
  </code></pre>
  
  <p>What's the solution if we insist to use the format of "square = function (n)"?</p>