[Vuejs]-Vue TypeError: "Cannot read property 'Bd' of undefined"

PS: This is an Chrome Extension for the Google Calendar.

I solved this Issue, by loading the script-Tags for vue.js in the End of my script.
I am manipulating the DOM to inject a Button in the Google Calendar, and when i load the vue.js script after the DOM-Manipulation, then it works. (i dont know why)

Can anyone explain me the behavior??