Match Whitespace - Why doesn't \s* work as well as \s+?

JavaScript
1

Tell us what’s happening:

  1. (*) = 0 or more matches.
  2. (+) = 1 or more matches.

Why shouldn’t either character behave in the same way?

I did test these in CodePen and \s+ returns all the whitespace in a string while \s* returned all the characters as “” and white space as " " plus one additional “”. What is \s* tracking as the last “”?

Your code so far


let sample = "Whitespace is important in separating words";
let countWhiteSpace = /\s+/g; // Change this line
let result = sample.match(countWhiteSpace);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.87 Safari/537.36.

Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/regular-expressions/match-whitespace

2

There are 0 whitespace characters between the letters, so they count as a match for /\s*/g. There’s also 0 whitespace characters right before the very first and right after the very last letter of the string.

3

Hi @kevcomedia,

let sample = “h h”;
let countWhiteSpace = /\s*/g; // Change this line
let result = sample.match(countWhiteSpace);
console.log(result)
//["", " ", “”, “”]

  1. “” : 0 white space before the first character of the string
  2. " " : 1 white space between the characters
  3. “” : 0 white space
  4. “” : 0 white space after the last character of the string

Shouldn’t the result return ["", " ", “”]?

5

I see what you mean. It seems that it also captures the empty string between spaces and the next letter. See https://regex101.com/r/9GWpLv/1. In particular the dashed line after the blue highlight in the string

1 Like
6

That’s interesting! can you share your pen?

7

https://codepen.io/SuperBeowulf/pen/qKKvrd?editors=0012

8

That’s a pretty cool tool. This makes it so much easier to visualize.

It is interesting though that /\s*\ of “h h” will find 0 whitespace before the 2nd h but not after the 1st h.