javascript extending functions
<p>I read a book about how to extend object with a method:
I was confused with the following code:</p>

<blockquote>
  <blockquote>
    <p>Array.prototype._m=Array.prototype.m ||<br/>
    (  Array.prototype.m=function(){<br/>//codes<br/>})<br/>
    Object.prototype.m=Array.prototype._m<br/></p>
  </blockquote>
</blockquote>

<p>It's said that the code like this is safe and high compatibility.<br/>
But I can't see how it works <br/>
And why </p>

<blockquote>
  <blockquote>
    <p>Array.prototype.m=function(){}</p>
  </blockquote>
</blockquote>

<p>is not safe enough
Thanks a lot!</p>
