During Web Dev Refreshing my website causes an error with Javascript.

In specific when I first load the website my javascript disc access works fine (correction: It breaks most of the time), it grabs the specific json file I need and at the correct index. However, upon a refresh, the script runs, and breaks (if it was working before). This wonkiness is creating a big problem for the website I am working on as I would like it to work. (To note: the Javascript loads without any errors on Chrome and other browsers).