How can I check if a javascript file exist without downloading it in bash or python

You can use python urllib module to check file existence in a given URL. Here's a sample code. The results are saved inside the "results" dictionary.

from urllib.request import urlopen
urls = ['https://www.codecademy.com/cdn-cgi/challenge- platform/h/g/scripts/alpha/invisible.js','https://www.codecademy.com/idontexist.js']
results={}
for url in urls:
    try:
        ret = urlopen(url)
        if ret.code == 200:
            state="Exists"
            print(url+' : {}'.format(state))
    except:
        state="Not exists"
        print(url+' : {}'.format(state))

    results[url]=state