Why my example with selecting a fir doesn't work?

[8Observer8]

Why my example with selecting a fir doesn't work? It shows nothing: https://plnkr.co/edit/vFbnHF3gBIBCSEdv

But when I place my example on Glitch it works:

• Demo: https://select-fir-by-mouse-webgl-js.glitch.me/
• Source: https://glitch.com/edit/#!/select-fir-by-mouse-webgl-js