Conditionally replacing string with Regular Expression

Question

In a node.js server I need to convert URL addresses using JavaScript as follows:

Example 1:

hostA/blah/dir1/name/id.js?a=b --> name.hostC/dir2.js?guid=id&a=b

Example 2:

hostB/dir1/name/id.js --> name.hostC/dir2.js?guid=id

The conversion is done with string.replace using regular expressions detailed inside a configuration file.

So far I have:

url.replace(/.*\\/dir1\\/(.*)\\/\\(d{2})\\.js?:(?=\?)(.*)/, "$1.hostC\/dir2.js?guid=$2");

The replacing string specifies ?guid=id. How do I alter the expression or the replacing string so that &originalQueryString (note the ampersand) will be added in case of example 1 and nothing added in case of example 2?

@ThomasAyoub In the first test case there, it needs to change the second ? to a & (hence the difficulty). — castletheperson
– castletheperson, Commented May 19, 2016 at 7:31

Michael Gaskill · Accepted Answer · 2016-05-19 11:52:45Z

1

This will work for your examples:

text.replace(/.*?\/dir1\/([^\/]+)\/(.*?)\.js\??(.*)/i, "$1.hostC/dir2.js?guid=$2&$3").replace(/&$/, "")

You can change the regex options to include 'g' or 'm', if called for in your implementation.

edited May 19, 2016 at 11:52

answered May 19, 2016 at 7:46

Michael Gaskill

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1 Comment

Dondey Over a year ago

This doesn't answer my question, but this is what I ended up doing since it looks like a single expression to do what I want is too complex.

nu11p01n73R · Accepted Answer · 2016-05-19 07:44:08Z

0

You can write something like

/([^/]+)\/([^./]+)\.js(?:\?(.*))?$/

Example

> "hostA/blah/dir1/name/id.js".replace(/([^/]+)\/([^./]+)\.js(?:\?(.*))?$/, "$1.hostC/dir2.js?guid=$2&$3")
< "hostA/blah/dir1/name.hostC/dir2.js?guid=id&"

> "hostA/blah/dir1/name/id.js?a=b".replace(/([^/]+)\/([^./]+)\.js(?:\?
(.*))?$/, "$1.hostC/dir2.js?guid=$2&$3")
< "hostA/blah/dir1/name.hostC/dir2.js?guid=id&a=b"

If the trailing & is a problem, you can break the regex into two statements,

< "hostA/blah/dir1/name/id.js".replace(/([^/]+)\/([^./]+)\.js$/, "$1.hostC/dir2.js?guid=$2")
> "hostA/blah/dir1/name.hostC/dir2.js?guid=id"

> "hostA/blah/dir1/name/id.js?a=b".replace(/([^/]+)\/([^./]+)\.js(?:\?(.*))$/, "$1.hostC/dir2.js?guid=$2&$3")
< "hostA/blah/dir1/name.hostC/dir2.js?guid=id&a=b"

edited May 19, 2016 at 7:44

answered May 19, 2016 at 7:34

nu11p01n73R

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7 Comments

castletheperson Over a year ago

They don't want a trailing & in the url. nothing added in case of example 2

Thomas Ayoub Over a year ago

What about hostA/blah/dir1/name/id.js?a=b?b=c ?

nu11p01n73R Over a year ago

@ThomasAyoub I assume that is not a valid url

nu11p01n73R Over a year ago

The removal of the trailing & is quite complex to write in a single regex, because it is a new character inserted which you cannot capture from the input string, but have to be derived.

castletheperson Over a year ago

I would suggest a simple if statement that removes any trailing & if it is there. if (url.charAt(url.length - 1) === "&") url = url.substr(0, url.length - 1);

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