JavaScript Regex String with one asterisk

Question

I want to check if a string hast 0...n whitespace, one * and 0...n whitespace.

The pattern

 var derefpatt = new RegExp("\\s*\\*\\s*");  
 var res2 = derefpatt.test(string);

is true if string is " ** " but it should be only true if string is " * "

What is wrong?

Regards

Alex

is n the same for both whitespace ?

CMPS
– CMPS

2015-04-10 17:07:12 +00:00
Commented Apr 10, 2015 at 17:07 — CMPS
– CMPS, Commented Apr 10, 2015 at 17:07

Federico Piazza · Accepted Answer · 2015-04-10 17:14:32Z

2

For:

0...n whitespace -> \s*
one * -> \*
0...n whitespace -> \s*

You can use this regex (notice the usage of anchors ^ and $):

^\s*\*\s*$

Regular expression visualization

On the other hand, if you want the same amount of spaces, you can use:

^(\s*)\*\1$

edited Apr 10, 2015 at 17:14

answered Apr 10, 2015 at 17:06

Federico Piazza

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2 Comments

knowledge Over a year ago

Thanks... var derefpatt = new RegExp("^\\s*\*\\s*$"); works. But why "\\s*\*\\s*" without ^ and $ doesn't work?

RyNo Over a year ago

Because RegExp.test() doesn't check whether the whole string matches, it checks for any substring within the string that matches and returns true if it finds any. Since there are 0 characters of whitespace between the asterisks, it fulfills the condition of 0 characters of whitespace after an asterisk.

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