Add leading and trailing slashes to string if needed using regex

Question

I'm having an issue, where I need to add leading and trailing slashes to string if it's not having them, or do nothing if string is already has it.

For example:

"/path" => "/path/"

"path/" => "/path/"

"path" => "/path/"

"/path/" => "/path/"

"/" => "/"

"" => "/"

I've tried to use this regular expression, but it's not adding trailing slash:

'/path'.replace(/(^\/?)|(\/?$)/, '/'); // output is "/path"

Have a look at this demo.

Wiktor Stribiżew
– Wiktor Stribiżew

2017-05-07 20:40:49 +00:00
Commented May 7, 2017 at 20:40 — Wiktor Stribiżew
– Wiktor Stribiżew, Commented May 7, 2017 at 20:40

Rick Hitchcock · Accepted Answer · 2017-05-07 20:41:12Z

7

[With thanks to Dmitry!]

This will work for your first 5 cases:

string.replace(/^\/?([^\/]+(?:\/[^\/]+)*)\/?$/, '/$1/');

You're then left with the null string, which you can handle using the OR operator (||):

string.replace(/^\/?([^\/]+(?:\/[^\/]+)*)\/?$/, '/$1/') || '/';

Snippet:

var RE = /^\/?([^\/]+(?:\/[^\/]+)*)\/?$/;

console.log('/path'.replace(RE, '/$1/') || '/');
console.log('path/'.replace(RE, '/$1/') || '/');
console.log('path'.replace(RE, '/$1/') || '/');
console.log('/path/'.replace(RE, '/$1/') || '/');
console.log('/'.replace(RE, '/$1/') || '/');
console.log(''.replace(RE, '/$1/') || '/');
console.log('path/with/embedded/slashes'.replace(RE, '/$1/') || '/');

edited May 7, 2017 at 20:41

answered May 7, 2017 at 20:22

Rick Hitchcock

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6 Comments

Dmitry Egorov Over a year ago

Perhaps, the path is supposed to have optional slashes in the middle as well. In such cases (e.g. some/longer/path) the suggested solution would fail.

Rick Hitchcock Over a year ago

That's a good point. The OP will have to respond if that's the case.

Dmitry Egorov Over a year ago

Yet, your solution may be extended to ^\/?([^\/]+(?:\/[^\/]+)*)\/?$ to cover such cases.

1ven Over a year ago

@DmitryEgorov correct, it may have optional slashes in the middle. Right now, I've ended up with that solution: 'path'.replace(/^\/?([^\/]+)\/?$/, '/$1/');. It will return double slashes for an empty and single slash input string. That case could be resolved by simple condition. But it's a little hacky

Rick Hitchcock Over a year ago

@DmitryEgorov, that's brilliant. Now updated, but if you want to post it yourself for credit, I'll delete my answer.

|

leonheess · Accepted Answer · 2022-11-14 18:44:29Z

0

Shorter:

string.replace(/^\/?([^/]+(?:\/[^/]+)*)\/?$/, '/$1/');

answered Nov 14, 2022 at 18:44

leonheess

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