Question

Unfortunately, findDate will also happily extract the nonsensical date 00-1-3000 from the string "100-1-30000" . A match may happen anywhere in the string, so in this case, it’ll just start at the second character and end at the second-to-last character.

If we want to enforce that the match must span the whole string, we can add the markers ^ and $ . The caret matches the start of the input string, while the dollar sign matches the end. So, /^\d+$/ matches a string consisting entirely of one or more digits, /^!/ matches any string that starts with an exclamation mark, and /x^/ does not match any string (there cannot be an x before the start of the string).

If, on the other hand, we just want to make sure the date starts and ends on a word boundary, we can use the marker \b . A word boundary can be the start or end of the string or any point in the string that has a word character (as in \w ) on one side and a nonword character on the other.

console.log(/cat/.test("concatenate"));
// → true
console.log(/\bcat\b/.test("concatenate"));
// → false

Note that a boundary marker doesn’t represent an actual character. It just enforces that the regular expression matches only when a certain condition holds at the place where it appears in the pattern.

This is a book about getting computers to do what you want them to do. Computers are about as common as screwdrivers today, but they contain a lot more hidden complexity and thus are harder to operate and understand. To many, they remain alien, slightly threatening things.