replace and increment integer value using a javascript regex

Question

Given the following string

XXXX Units[4].Test XXXX

I would like to replace each occurrence of Unit[x] with Unit[x+1].
I am trying to achieve this using a regular expression, as the name Units needs to be literally matched first.

I am trying something like this:

test.replace(/(?:Units\[|\_+)(\d+)/g, function(m, i) { return parseInt(m) + 1 })

My problem is that without positive lookbehind I cannot seem to match only the digits. I am trying to build the regex in such a way that only the digits form part of the capture group, and I can therefore replace them.

It's easy to do in c#, but the javascript match function works a little differently.

Despite the non capture specification of (?: the Units[ seems to form part of the match. Since javascript does not support look behind, I am at a loss as to how to complete this.

The first argument to the callback function is the entire match. The first group in the regex is the second argument. — Pointy
– Pointy, Commented Mar 21, 2016 at 15:10
(?: just means it's not in a capturing group, it's still in the overall substring that's parsed, and then your digits are in the first captured group. — Patrick Roberts
– Patrick Roberts, Commented Mar 21, 2016 at 15:10
Specifying a function as a parameter to String.prototype.replace() this may be of help to you. — Patrick Roberts
– Patrick Roberts, Commented Mar 21, 2016 at 15:15

anubhava · Accepted Answer · 2016-03-21 15:14:43Z

5

You need to group the part before number and use that back-reference in replacement later:

test = test.replace(/(Units\[)(\d+)/ig, function($0, $1, $2) {
      return $1 + (parseInt($2)+1); })

//=> XXXX Units[5].Test XXXX

Note use of $1 and $2 in the callback function where $1 represents value Units[ and $2 is the number after it.

answered Mar 21, 2016 at 15:14

anubhava

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