How to search replace with regex and keep case as original in javascript

Question

Here is my problem. I have a string with mixed case in it. I want to search regardless of case and then replace the matches with some characters either side of the matches.

For example:

var s1 = "abC...ABc..aBC....abc...ABC";
var s2 = s.replace(/some clever regex for abc/g, "#"+original abc match+"#");

The result in s2 should end up like:

"#abC#...#ABc#..#aBC#....#abc#...#ABC#"

Can this be done with regex? If so, how?

Hm

Answer 1

This can be done using a callback function for regex replace.

var s1 = "abC...ABc..aBC....abc...ABC";

var s2 = s1.replace(/abc/ig, function(match) {
  return "#" + match + "#";
});

console.log(s2);

Kidney

Sounds promising, can you give me an example – Hm

@Hm mine isn't briliant? ;-) It's shorter and probably faster ;-) – Roca

@JanDvorak Your answer is equally brilliant, but IMHO callback functions provide more flexibility to operate over the matches as compared to expressions with backreferences. – Kidney

@Kidney I agree that callbacks are very flexible and good to learn ;-) – Roca

@JanDvorak Callbacks may provide more flexibility and are good to know but they are slower when compared to using backreferences. See this JSPerf – Thigmotropism

@Thigmotropism that's why I wrote my own answer in the first place. – Roca

@JanDvorak I thought yours would be faster - it's good to have proof! – Thigmotropism

This one works for me, the answer with a back-reference not. – Orvie

Answer 2

This can be done using a back-reference:

var s2 = s.replace(/your complex regex/g, "#$&#");

The back-reference $& brings in the entire match. If you want to match "abc" in any case:

var s2 = s.replace(/abc/ig, "#$&#");

If you only want to bring in part of a larger pattern, you can refer to it by its group number:

var s2 = s.replace(/some (part) of a string/ig, "#$1#");

Groups are numbered by their opening parenthesis, from left to right, from $1 to $9.

Roca

what would be the regex expression? – Hm

@Hm the same as yours. I assumed "abc" was just a placeholder for something else that you already knew how to match. – Roca

Can you show this example on regex101? Does it also work with the python or php settings? – Lest

Answer 3

You can also do this

yourString.replace(/([a-z]+)/ig, "#$1#")

Irrupt

This replaces all occurances with #abC# which is not what I want – Hm

@Hm you can remove g if you dont want to match all occurances – Irrupt