Question

Can anybody point it out?

1. /^([a-zA-Z]+)/
2. /\d|M|H/
3. RegExp.$1

Answer 1

1.

/^([a-zA-Z]+)/

^             # match the start of the input string
(             # start capture group 1
  [a-zA-Z]+   #   match one or more from the set {a..z,A..Z} 
)             # end capture group 1

2.

/\d|M|H/

\d  # match a digit: {0..9}
|   # OR
M   # match the literal 'M'
|   # OR
H   # match the literal 'H'

which, as @Tim suggested in the comments, could better be written as: [\dMH]

3.

RegExp.$1 is probably not a regex (at least, it can’t match anything). It’s likely a language construct.