Text Processing with JavaScript

Recipe 30

Treating Multiple Characters as a Single Unit with the Capturing Group

Task

Suppose you want to search an archive of documents and retrieve those that mention a date in August. The only clue you have is that the date comes in four different styles. For example: “August 16,” “August 16th,” “Aug 16,” or “Aug 16th.”

To match such a date with regex, you need a way to make “ust” in “August” and “th” in “16th” optional.

Solution

To make certain letters optional, group them by enclosing them in parentheses and place a question mark after the group:

part_2/capturing_group_p1/capturing_group_p1_ex1.js

const re = /\bAug(ust)?\s\d{1,2}(st|nd|rd|th)?\b/;

// Grouping allows matching many alternatives
re.test("Aug 16"