title: Is an argument of a function declared when no value is passed?
body: <p>I have a general question about the Javascript language.
  When I define a function like that:</p>
  
  <pre><code>{
    var some_func = function(arg1, arg2) {
      //some code here
    }
  }
  </code></pre>
  
  <p>and I pass only the first argument to the function like that:</p>
  
  <pre><code>var variable = some_func(a1);
  </code></pre>
  
  <p>is the second argument <code>arg2</code> defined but with value of <code>undefined</code> or is it entirely <code>undefined</code></p>
  
  <p>Or to paraphrase it: are the parameters of the function simply defined as variables, or object properties, when the function is defined, or is there some dynamic declaration mechanism behind the scenes?</p>