Simon Willison's Weblog: instanceofhttp://simonwillison.net/2009-01-12T10:55:07+00:00Simon Willisoninstanceof considered harmful (or how to write a robust isArray2009-01-12T10:55:07+00:002009-01-12T10:55:07+00:00https://simonwillison.net/2009/Jan/12/isarray/#atom-tag
<p><strong><a href="http://thinkweb2.com/projects/prototype/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/">instanceof considered harmful (or how to write a robust isArray</a></strong></p>
JavaScript’s instanceof operator breaks when dealing with objects that may have been created in a different document or frame, since constructors are unique to each frame. Instead, you can check for arrays using the default Object.toString method which the JS spec guarantees will return [object Array].
<p>Tags: <a href="https://simonwillison.net/tags/arrays">arrays</a>, <a href="https://simonwillison.net/tags/frames">frames</a>, <a href="https://simonwillison.net/tags/instanceof">instanceof</a>, <a href="https://simonwillison.net/tags/javascript">javascript</a>, <a href="https://simonwillison.net/tags/tostring">tostring</a></p>