How to query MongoDB with %like%?

I want to query something as SQL’s like query:

select * 
from users 
where name like '%m%'

How to do the same in MongoDB?

db.users.find({name: /a/})  //like '%a%'
db.users.find({name: /^pa/}) //like 'pa%'
db.users.find({name: /ro$/}) //like '%ro'

Or using Mongoose:

db.users.find({'name': {'$regex': 'sometext'}})