regex-cheatsheet.js

// Tool to nicely validate your regex: http://www.regexpal.com/

// Empty java regex
//g

// Single letter
/T/g

// Testing 
/T/g.test('T')

// The rest of the examles do not contain '//g'

// Exact string - 'Tomek'
Tomek

// Line starting with given string - 'Tomek is the author'
^Tomek

// Single digit - '1'
\d

// Single, any chara character
.

// Exactly one digit in the begining - '1'
^\d{1}

// Exactly one or two digit in the begining - '1'
^\d{1,2}

// Two or more digit in the begining - '234'
^\d{2,}

// Zero or more digits
\d*
  
// One or more digits
\d+
  
// Zero or one digit
\d?
  
// Only one of given characters in the begining - 'c'
^[abc]

// Or another way
^[a-c]

// One of the choices - 'cd'
ab|cd

// Groups: catching the number - 'I am 31 yers old'
(\d{1,})


// Date validation - '1970-01-01T10:00:00Z'
/\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z/g