title: Raise event whenever object property is added in Javascript?
body: <p>I have a Javascript  object : </p>
  
  <p><code>var obj={...};</code></p>
  
  <ul>
  <li><p>How can I execute a function whenever a new property is added/changed : </p>
  
  <p>For example:<code>obj["newItem"]=3;</code></p></li>
  <li><p>is there any way also for arrays ? (excpet override <code>push</code> in prototype)</p></li>
  <li><p>is there any way to do it also for assign a different object to the same variable ?</p>
  
  <p>example : </p>
  
  <pre><code>var obj={...};
      obj={...}; //redifine
  </code></pre></li>
  </ul>