Sean Corfield recently blogged about the choice to use IsDefined vs. structKeyExists when trying to determine if a scoped variable (session, application, request, form url etc), exists or not.

Sean talks about how certain dot noted variables will or won’t be seen with IsDefined, BUT I found the fact that IsDefined looks for ANY possible definition even when the variable you’re searching for has been scoped.

Read his blurb to get the full effect.


  • MarcusJT

    The first paragraph is an incomplete sentence… *what* are you trying to determine?!

  • jonese

    fixed sorry about that, must have gotten lost in my cut / paste.

Special Offer
Free course!

Git into it! Bonus course Introduction to Git is yours when you take up a free 14 day SitePoint Premium trial.