If you don’t want fields such as “[Online]”, “Available: …” appear in IEEEtran bibliography items:

1. Go to installation folder of IEEEtan bst.
(on my Mac OS with Texlive, the folder is /usr/local/texlive/2016/texmf-dist/bibtex/bst/IEEEtran)

2. Backup and then edit IEEEtran.bst, search “FUNCTION XXX” (XXX could be “inproceedings”, “inbook”, etc.), and comment out “format.url output”

3. run “texhash”

4. recompile .bib and .tex files.