Common regular expressions

Angelos Chalaris · JavaScript, String, Regexp · Nov 9, 2022

Exact string match

  • Use the ^ and $ anchors to match the start and end of the string, respectively.
  • Add the string you want to match in-between the two anchors.
const regexp = /^abc$/;
// Where 'abc' is the exact string you want to match

Match empty string

  • Use the ^ and $ anchors to match the start and end of the string, respectively.
  • Do not add any characters in-between to match an empty string.
const regexp = /^$/;

Match whitespace sequences

  • Use the \s meta-sequence to match any whitespace character, including spaces, tabs, newlines, etc.
  • Use the + quantifier to match one or more occurrences of the previous character.
  • Add the global flag (g) to match all occurrences of the pattern in the string.
const regexp = /\s+/g;

Match line breaks

  • Depending on the environment, line breaks can be represented in different ways.
  • Use the \r character to match carriage returns, the \n character to match newlines, and the \r\n sequence to match carriage returns followed by newlines.
  • Add the global (g) and multiline (m) flags to match all occurrences of the pattern in the string.
const regexp = /\r|\n|\r\n/gm;

Match non-word characters

  • Use negation (^) to match any character that is not a word character (\w) or a whitespace character (\s).
  • Add the global flag (g) to match all occurrences of the pattern in the string.
  • Add the ignore case flag (i) to match both uppercase and lowercase characters.
const regexp = /[^\w\s]/gi;

Match alphanumeric, dashes and hyphens

  • Use the ^ and $ anchors to match the start and end of the string, respectively.
  • Use the a-zA-Z0-9- pattern to match any alphanumeric character, dashes and hyphens.
  • Use the + quantifier to match one or more occurrences of the previous character.
  • Particularly useful when matching URL slugs.
const regexp = /^[a-zA-Z0-9-_]+$/;

Match letters and whitespaces

  • Use the ^ and $ anchors to match the start and end of the string, respectively.
  • Use the a-zA-Z\s pattern to match any letter and whitespace character.
  • Use the + quantifier to match one or more occurrences of the previous pattern.
const regexp = /^[A-Za-z\s]+$/;

Pattern not included

  • Use the ^ and $ anchors to match the start and end of the string, respectively.
  • Use a negative lookahead (?!) to match any character that is not followed by the pattern you want to exclude.
  • Add the global flag (g) to match all occurrences of the pattern in the string.
  • To ensure more than one pattern is not included, use the | character to separate them.
const regexp = /^((?!(abc|bcd)).)*$/;
// Where 'abc' and 'bcd' are pattern you want to exclude

Text inside brackets

  • Use the \( and \) characters to match the opening and closing brackets, respectively.
  • Use a capturing group between the two and exclude the closing parenthesis character.
  • Use the + quantifier to match one or more characters, as needed.
  • Add the global flag (g) to match all occurrences of the pattern in the string.
  • Replace \( and \) with \[ and \] to match square brackets and with \{ and \} to match curly brackets.
const regexp = /\(([^)]+)\)/g;

Validate GUID/UUID

  • Use the ^ and $ anchors to match the start and end of the string, respectively.
  • Validate each segment of the GUID/UUID separately using numeric character ranges and quantifiers.
const regexp = /^(0?[1-9]|[12][0-9]|3[01])[\/\-](0?[1-9]|1[012])[\/\-]\d{4}$/;

Validate date format (DD/MM/YYYY)

  • Use the ^ and $ anchors to match the start and end of the string, respectively.
  • Validate each segment of the date separately using numeric character ranges and quantifiers.
  • Alter the order of the segments and separators to match different formats.
const regexp = /^(0?[1-9]|[12][0-9]|3[01])[\/\-](0?[1-9]|1[012])[\/\-]\d{4}$/;

Chunk string into n-size chunks

  • Use the .{1,n} quantifier to match any character between 1 and n times.
  • Add the global flag (g) to match all occurrences of the pattern in the string.
const regexp = /.{1,2}/g;
// Where '2' is the number of characters per chunk

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