regex - JavaScript regular expression with capturing parentheses -

i have paragraph:

<p>first second third</p>

and want wrap second word in span so:

<p>first <span>second</span> third</p>

if this:

text.replace(/\s(\w+)\s/, '<span>$1</span>');

the space characters before , after word disappear. why? doing wrong? thought /\s(\w+)\s/ captures word not spaces.

see here: http://jsfiddle.net/simevidas/tptzv/

the spaces stripped away because they're part of entire match. capture remembers substitute replacement string via backreferences.

if javascript supported both lookahead , lookbehind assertions this:

text.replace(/(?<\s)(\w+)(?=\s)/, '<span>$1</span>');

but doesn't, can try capturing spaces (separately word you're wrapping) , putting them in instead:

text.replace(/(\s)(\w+)(\s)/, '$1<span>$2</span>$3');

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