How does this JavaScript RegExp work?

Question

I am lost about how this works:

x=x.replace(/^\s+|\s+$/g,"");

What is the pipe( | ) for ?

@PeeHaa - Ah, yes( I need coffee!). what of the /g part?

Caffeinated
– Caffeinated

2012-03-26 19:59:52 +00:00
Commented Mar 26, 2012 at 19:59 — Caffeinated
– Caffeinated, Commented Mar 26, 2012 at 19:59
I see you're reading the same book that I am :)

Aditya M P
– Aditya M P

2013-09-07 11:00:32 +00:00
Commented Sep 7, 2013 at 11:00 — Aditya M P
– Aditya M P, Commented Sep 7, 2013 at 11:00

Tim Pietzcker · Accepted Answer · 2012-03-26 20:00:49Z

5

The pipe means "or".

So your regex matches

^    # the start of the string
/s+  # followed by whitespace (one or more characters)
|    # or
/s+  # whitespace
$    # followed by the end of the string

The /g (global) modifier applies the regex to all matches in the string, not just the first one.

answered Mar 26, 2012 at 20:00

Tim Pietzcker

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1 Comment

Halcyon Over a year ago

The modifier is just g, the / is part of the delimiter which indicates the end of the regular expression.

Halcyon · Accepted Answer · 2012-03-26 20:00:25Z

3

It means or. The part to the left matches any leading spaces (^), the part to the right matches any trailing space ($). The g modifier allows this matching to be applied more than once, which is useful if you're expecting both trailing and leading space.

Basically this regex trims whitespace.

An alternative way to write this regex is, using the new RegExp construct:

x = x.replace(new RegExp("^\s+|\s+$", "g"), "");

If find this notation more readable because you don't need your delimiters (/) and your modifier is separated.

answered Mar 26, 2012 at 20:00

Halcyon

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Comments

Cheeso · Accepted Answer · 2012-03-26 20:02:17Z

2

It's an alternation construct.

The regex says "either the beginning-of-string followed by one or more whitespace characters, OR, one or more whitespace characters followed by end-of-string".

I think that is the intent, anyway. I'm not sure now that I read JaredPar's answer.

If I were writing this I would use parens to make it explicit.

x = x.replace(/(^\s+|\s+$)/g,"");

edited Mar 26, 2012 at 20:02

answered Mar 26, 2012 at 19:59

Cheeso

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1 Comment

Tim Pietzcker Over a year ago

This is incorrect. ^ and $ match the end of the string, not the end of the line, unless the /m modifier is used, which it isn't.

Bogdan Emil Mariesan · Accepted Answer · 2012-03-26 19:59:16Z

1

That "pipe" in regex stands for an "OR" so your regex will either match the pattern before the "pipe" either the pattern after the "pipe"

answered Mar 26, 2012 at 19:59

Bogdan Emil Mariesan

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BoltBait · Accepted Answer · 2012-03-26 19:59:24Z

1

The pipe character "|" represents "or".

answered Mar 26, 2012 at 19:59

BoltBait

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Siva Charan · Accepted Answer · 2012-03-26 20:01:13Z

1

Pipe is represent OR
/g represents Global
\s represents Space

answered Mar 26, 2012 at 20:01

Siva Charan

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1 Comment

Code Jockey Over a year ago

\s means "whitespace character" (which includes standard space, tab, carriage return, line feed, and more obscure ones as well)

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