title: is JS able to overwrite Object's Getter method?
body: <p>everyone:</p>
  
  <p>as we all know, getting a nonexistent value from Object will got a "undefined", is there any way to throw an error instead of return a <code>undefined</code>?</p>
  
  <p>for instance:</p>
  
  <pre><code>var a= {example:"example"};
  //do something here
  
  a.b  //error throw instead of "undefined"
  </code></pre>
  
  <p>thx very much for helping. </p>