Wrong content type on Windows when using StaticFiles

[ZeroIntensity]

i'm using fastapi, but this issue originates from starlette.

when using StaticFiles on windows, the Content-Type header for js files isn't application/javascript, but instead text/plain. code below to reproduce:

import uvicorn
from fastapi import FastAPI
from fastapi.staticfiles import StaticFiles  # same as starlette.StaticFiles

app = FastAPI()

app.mount("/static", StaticFiles(directory="./"), name="static")  # put something like a blank "a.js" in the current directory to test

if __name__ == '__main__':
    uvicorn.run(app, port = 8080)

import requests

print(requests.get('http://127.0.0.1:8080/static/a.js').headers['content-type'])

i tested the above on linux (ubuntu 20.04 lts), and it works just fine. this seems to only occur on windows

this also seems to be only for js files, i tested it with html and css and it returned the correct content type.

[Kludex]

This was already mentioned on #829.