Regular Expressions - Remove Whitespace from Start and End

JavaScript
1

I’m not sure why my solution doesn’t work. In my mind wsRegex begins at the beginning of the string, matches with anything that is not a whitespace, then it matches with anything that is a whitespace, then it matches with anything that is not whitespace and finally returns everything it matched with to result. I know the solution posted finds the whitespaces and replaces them with nothing. My idea for the solution was find everything that is not a whitespace and return that (except for whitespaces in the middle of the word).

Your code so far

let hello = "   Hello, World!  ";
let wsRegex = /^\S*\s*\S*$/g; // Change this line
let result = hello.match(wsRegex); // Change this line

console.log(result);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/103.0.0.0 Safari/537.36

Challenge: Regular Expressions - Remove Whitespace from Start and End

Link to the challenge:

2

let hello = " Hello, World! ";
let wsRegex = /^\S*\s*\S*$/g;

Your regular expression is saying:

  • At the beginning of the string match a non-whitespace character zero or more times
  • Then, match a whitespace character zero or more times
  • And at the end of the string match a non-whitespace character zero or more times
  • global flag activated (return all possible matches)

Your hello string begins with a whitespace character, that’s why your regex can’t find a match from the very beginning.

3

Ah I see, but why won’t it keep searching until it finds a non-whitespace character at the beginning? Is the string not evaluated in a left-right fashion?

4

Your regex is trying to exactly match as I described to you. If it fails to match even for the first type of character, it will totally fail.

5

Ah I see, thank you for clearing that up! Also is there a way to evaluate the whitespaces but not include them in the match? Like could I use a positive lookahead to evaluate white spaces at the beginning? That way my function won’t be stopped.

6

Yes, there is. But, if you are really at the beginning of regular expressions, I would recommend you to learn the basics. FreeCodeCamp is really a good platform to start fresh in coding.

In this case, what you want is to match a first non-whitespace character one or more times, match a whitespace character, and finally match a non-whitespace character one or more times.

Just try without the caret (^) and the dollar sign ($). Those are restricting you.

7

I tried let wsRegex = /(?=\s*)\S*\s\S*/g; and result = [ ’ ‘, ’ ‘, ’ Hello,’, ’ World!’, ’ ', ’ ’ ]. Why are there spaces at the beginning and the end if I’m not matching those?

8

Try the website regexr.com . There you can simulate more easily your regular expressions, and see each change immediately.

9

Will do, thanks! I figured out why it wasn’t working. The positive lookahead only works after you have something that matched. At least thats what I found.

1 Like
10 
/(?=\s*)\S*\s\S*/g

You wrote a positive lookahead before the expression you want to find. In that position, you would have to write a positive lookbehind:

/(?<=\s*)\S*\s\S*/g
11

There are always several ways to achieve the same coding goal.

P.S.: I do not know if I confused you, but:
* matches a preceding character zero or more times
+ matches a preceding character one or more times

12

No confusion! Thanks for helping me! I didn’t know there was a lookbehind. That should do the trick :grin:. Talking through this with you has really helped me understand it more! Thx!

1 Like
13

No problem :slight_smile: . If you passed the challenge and don’t have more questions on this subject, please select this topic question as solved. Thank you

14

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