javascript - Is there a difference between sg and s+g? - Stack Overflow

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When we have a string that contains space characters:

var str = '  A B  C   D EF ';

and we want to remove the spaces from the string (we want this: 'ABCDEF').

Both this:

str.replace(/\s/g, '')

and this:

str.replace(/\s+/g, '')

will return the correct result.

Does this mean that the + is superfluous in this situation? Is there a difference between those two regular expressions in this situation (as in, could they in any way produce different results)?

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Update: Performance comparison - /\s+/g is faster. See here:

When we have a string that contains space characters:

var str = '  A B  C   D EF ';

and we want to remove the spaces from the string (we want this: 'ABCDEF').

Both this:

str.replace(/\s/g, '')

and this:

str.replace(/\s+/g, '')

will return the correct result.

Does this mean that the + is superfluous in this situation? Is there a difference between those two regular expressions in this situation (as in, could they in any way produce different results)?

---

Update: Performance comparison - /\s+/g is faster. See here: http://jsperf.com/s-vs-s

• javascript
• regex

Share Improve this question Follow edited May 11, 2011 at 12:44 Šime Vidas asked May 11, 2011 at 12:39 Šime VidasŠime Vidas 186k6565 gold badges286286 silver badges391391 bronze badges 4

• 1 vidas stackoverflow.com/questions/5963182/… I bet this is what made you ask this question ;) (your comment on the answer) – user657496 Commented May 11, 2011 at 12:46
• 2 I can imagine \s+ is faster, because it can replace chunks of whitespace, whilst \s must replace each white space separately? – KooiInc Commented May 11, 2011 at 12:48
• 1 @KooiInc: Correct, because it matches/replaces fewer times. – BoltClock Commented May 11, 2011 at 12:49
• I suggest you look at this friend's answer. – user12829430 Commented Sep 10, 2021 at 8:50

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4 Answers 4

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In the first regex, each space character is being replaced, character by character, with the empty string.

In the second regex, each contiguous string of space characters is being replaced with the empty string because of the +.

However, just like how 0 multiplied by anything else is 0, it seems as if both methods strip spaces in exactly the same way.

If you change the replacement string to '#', the difference becomes much clearer:

var str = '  A B  C   D EF ';
console.log(str.replace(/\s/g, '#'));  // ##A#B##C###D#EF#
console.log(str.replace(/\s+/g, '#')); // #A#B#C#D#EF#

\s means "one space", and \s+ means "one or more spaces".

But, because you're using the /g flag (replace all occurrences) and replacing with the empty string, your two expressions have the same effect.

In a match situation the first would return one match per whitespace, when the second would return a match for each group of whitespaces.

The result is the same because you're replacing it with an empty string. If you replace it with 'x' for instance, the results would differ.

str.replace(/\s/g, 'x') will return 'xxAxBxxCxxxDxEF '

while str.replace(/\s+/g, 'x') will return 'xAxBxCxDxEF '

because \s matches each whitespace, replacing each one with 'x', and \s+ matches groups of whitespaces, replacing multiple sequential whitespaces with a single 'x'.

+ means "one or more characters" and without the plus it means "one character." In your case both result in the same output.

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