【JavaScript】URL形式もしくは未入力を許容する正規表現
/^(https?:\/\/[\w!?/+\-_~;.,*&@#$%()'[\]]+)?$/
[https://qiita.com/BRSF/items/2a83af4e605019e8c2fe:embed:cite]
[https://qiita.com/str32/items/a692073af32757618042:embed:cite]
/^(https?:\/\/[\w!?/+\-_~;.,*&@#$%()'[\]]+)?$/
[https://qiita.com/BRSF/items/2a83af4e605019e8c2fe:embed:cite]
[https://qiita.com/str32/items/a692073af32757618042:embed:cite]