Optional string in RegExp

Question

I want to catch if the url is a blog page or not. A blog page can be:

/blog
/blog/page/1
/blog/page/143

So, page/pageNumber is optional. How can I create a regular expression that being tested returns true if the url is a blog page?

I created the regex for urls containing /page/ string and it seems to work fine:

/\/blog\/page\/[1-9]([0-9]*)/

Example:

> /\/blog\/page\/[1-9]([0-9]*)/.test("/blog/page/1")
true
> /\/blog\/page\/[1-9]([0-9]*)/.test("/blog/page/0")
false
> /\/blog\/page\/[1-9]([0-9]*)/.test("/blog/page/30")
true

But how can I set /page/number to be optional?

I tried:

/\/blog(\/page\/[1-9]([0-9]*))?/

This returns true for incorrect urls:

> /\/blog(\/page\/[1-9]([0-9]*))?/.test("/blog/p")
true

@dandavis /blog/1-my-interesting-post is not the same with /blog/page/1. — Ionică Bizău
– Ionică Bizău, Commented Jun 25, 2014 at 7:57

Scimonster · Accepted Answer · 2014-06-25 07:54:27Z

1

You should add an end marker ($) so that it stops checking.

> /\/blog(\/page\/[1-9]([0-9]*))?$/.test("/blog/p")
false
> /\/blog(\/page\/[1-9]([0-9]*))?$/.test("/blog/page/1")
true
> /\/blog(\/page\/[1-9]([0-9]*))?$/.test("/blog/page/0")
false
> /\/blog(\/page\/[1-9]([0-9]*))?$/.test("/blog/page/30")
true
> /\/blog(\/page\/[1-9]([0-9]*))?$/.test("/blog")
true

answered Jun 25, 2014 at 7:54

Scimonster

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Comments

anubhava · Accepted Answer · 2014-06-25 07:56:20Z

1

You can use this regex to make /page/num optional:

/^\/blog(\/page\/\d+)?\/?$/

answered Jun 25, 2014 at 7:56

anubhava

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4 Comments

anubhava Over a year ago

Yes it won't and that is not in the requirements either.

Robby Cornelissen Over a year ago

It will still match /blog/p and /blog/page. Since the Javascript test() method is satisfied with a partial match.

anubhava Over a year ago

Yes true, have added anchors now to avoid that situation.

Ionică Bizău Over a year ago

@anubhava Also, /blog/page/0 shouldn't be matched. Anyways, thank you, all!

Robby Cornelissen · Accepted Answer · 2014-06-25 08:02:41Z

1

You want to add markers for the start (^) and end ($) of the string. In it's current form, your check will also return true if it only matches part of the string.

/^\/blog(\/page\/[1-9]([0-9]*))?$/

Check out this fiddle.

edited Jun 25, 2014 at 8:02

answered Jun 25, 2014 at 7:55

Robby Cornelissen

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Comments

Avinash Raj · Accepted Answer · 2014-06-25 08:12:49Z

0

You could use non capturing groups for this,

^\/blog(?:\/page(?:\/[1-9]\d*)?)?$

edited Jun 25, 2014 at 8:12

answered Jun 25, 2014 at 8:00

Avinash Raj

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3 Comments

dandavis Over a year ago

why would capturing matter when using /./.test() ?

Avinash Raj Over a year ago

@dandavis it won't capture anything.

Ionică Bizău Over a year ago

@AvinashRaj This will catch /blog/page/0 that is incorrect.

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