Reuse Patterns Using Capture Groups caret and dollar sign?

JavaScript
1

Tell us what’s happening:

I’m trying to understand why it’s necessary to put the caret (^) at the beginning and the dollar sign at the end ($). I managed to do all the challenge but those last two things I saw was in the hint and when I saw them, I stayed loading.

Your code so far


let repeatNum = "42 42 42";
let reRegex = /^(\d+)\s\1\s\1$/; // Change this line
let result = reRegex.test(repeatNum);
let result2 = repeatNum.match(reRegex);
console.log(result);
console.log(result2);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36.

Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/regular-expressions/reuse-patterns-using-capture-groups

1 Like
2

If you used .match and the .length === 1 assertion the challenge would’ve been solved as a function but since in this case you have some guarantees you only need the caret and the sign because:

1- You are guaranteed that the entire string only has numbers separated by spaces and nothing surrounding those numbers on both sides.
2- There’s always 1 space between numbers

So the pattern reads as follow

  • First match the beginning of the string
  • Then search for 1 or more digits together and save it as capture group #1
  • Match a space
  • Match the same number again referring to it as \1
  • Match a space
  • Match the same number again referring to it as \1
  • Finally, match the end of the string

This way you can assure that there’s no repetitions at the extremes of the string.

3 Likes
3

So, they are used to mark the beginning and end of the regex, right?

Es decir que sirven para marcar el comienzo y el final del regex, no? E

Español para ti, inglés para la comunidad jajajaja

4

Sí, para eso sirven

Yes that’s what they are for.

^ - Start
$ - End