Writing Fast, Memory-Efficient JavaScript
> Never use delete. Ever.<p>...<p>This is horrible advice. There are plenty of things you want to delete, like references to elements when you don't need them anymore. A quick search of the Closure Library, jQuery, Backbone, Knockout, Angular.js, and ember.js found many uses of delete. Burn this article in a fire.<p>As for the supposed performance difference, let's see a jsperf on that.<p>Edit found one:<p><a href="http://jsperf.com/delete-vs-undefined-vs-null/6" rel="nofollow">http://jsperf.com/delete-vs-undefined-vs-null/6</a><p>Delete is a little slower, certainly not enough to warrant the 'never' emphasis.