Question

How would you change this:

a-10-b-19-c

into something like this:

a-10-b-20-c

using regular expressions in Javascript?

It should also change this:

a-10-b-19

into this:

a-10-b-20

The only solution I’ve found so far is:

• reverse the original string -> "c-91-b-01-a"
• find the first number (with \d+) -> "91"
• reverse it -> "19"
• turn in into a number (parseInt) -> 19
• add 1 to it -> 20
• turn it into a string again (toString) -> "20"
• reverse it again -> "02"
• replace the original match with this new number -> "c-02-b-01-a"
• reverse the string -> "a-10-b-20-c"

I was hoping someone on SO would have a simpler way to do this… Anyone?

Answer 1

Here is a simple way.

var str = 'a-10-b-19-c';
str = str.replace(/(\d*)(?=(\D*)?$)/, +str.match(/(\d*)(?=(\D*)?$)/)[0]+1);

+str.match finds 19, adds 1 to it and returns 20. The + makes sure the answer is an int. str.replace finds 19 and replaces it with what str.match returned which was 20.

Explanation

• (\d*) – matches any digits
• (?=...) – positive lookahead, doesn’t change regex position, but makes sure that pattern exists further on down the line.
• (\D*)?$ – it doesn’t have to, but can match anything that is not a number multiple times and then matches the end of the string