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I have a problem with regular expression:

var regex = new RegExp('(^|\\s)' + clsName + '(\\s|$)');

What does (^|\\s) mean? Isn't it equal to (^|\s), what does (^|) mean?

Am I right, it means that the string should start with any letter or white space? I tried to test with browser and console.log but still can't get any solution.

In all tutorials \s is used to be a space pattern not \\s.

Ok i got it, the problem was:

When using the RegExp constructor: for each backslash in your regular expression, you have to type \\ in the RegExp constructor. (In JavaScript strings, \\ represents a single backslash!) For example, the following regular expressions match all leading and trailing whitespaces (\s); note that \\s is passed as part of the first argument of the RegExp constructor:

re = /^\s+|\s+$/g
re = new RegExp('^\\s+|\\s+$','g')
Cœur
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QbC
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2 Answers2

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(^|\\s) means: Start of the string (^) OR (|) a space \\s.

If clsName is "abc", for example, it builds the pattern (^|\\s)abc(\\s|$). That searches for "abc" at the start, middle, or end of the string, and it may be surrounded by spaces, so these are valid:

  • "abc"
  • "abc x"
  • "x abc"
  • "x abc y"

Note that here you are using a string to build a RegExp. JavaScript ignores escape characters it doesn't know - '\s' would be the same as 's', which isn't right.

Another option is to use word boundaries, but might fail on some case (for example, searching for btn would match for btn-primary):

var regex = new RegExp('\\b' + clsName + '\\b');

I'd also warn that clsName might contain regex meta-characters, so you may want to escape it.

Community
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Kobi
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Why not just split the string on " "?

var string = 'abc defh ij klm';
var elements = string.split(' ');
var clsName = 'abc';
elements.filter(function (el) {
    return el === clsName;
});

No need for a RegEx like the one you posted.

tenub
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