Enable microphone once per application load

I am adding voice input to a web app. I am using webkitSpeechRecognition (http://ift.tt/1FU2gky).

I've noticed that this popup occurs not only each application reload, but also every time I hit recognition.start(); (recognition = new webkitSpeechRecognition()) :

I am fine with the initial message, but since I will be having users use voice input a lot, I don't want to keep spamming them with this message.

How can I just have it show initially on web app load?