JS Regex lookbehind not working in firefox and safari

Question

I have this following regex which is working in chrome but causes an error in firefox or safari. I need to modify it to make it work. Can anybody help out a poor soul? Thanks in advance!

regex: /(?=<tag>)(.*?)(?<=<\/tag>)/

Basically, I have to match any char in between <tag> and </tag> and need to retain both tags. I used this expression as an argument to array.split.

input: "The quick brown <tag>fox</tag> jumps over the lazy <tag>dog</tag>"

operation: input.split(regex)

output: ["The quick brown ", "<tag>fox</tag>", " jumps over the lazy ", "<tag>dog</tag>"]

score 12 · Accepted Answer · edited Dec 28 '22 at 10:13

12

~~Firefox and~~ ^Has
Safari doesn't have support for lookbehind yet, you can use capture group ( used so that this the pattern on which we are splitting will be also be added in output ) and split on <tag> </tag>

let str = "The quick brown <tag>fox</tag> jumps over the lazy <tag>dog</tag>"

let regex = /(<tag>.*?<\/tag>)/

console.log(str.split(regex).filter(Boolean))

edited Dec 28 '22 at 10:13

Roko C. Buljan

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answered Oct 19 '19 at 04:46

Code Maniac

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1

It works. I appreciate the response. I realized I over engineered my initial regex. Cheers – webedward Oct 19 '19 at 04:55
No need using `g` modifier in this case since it is the default behavior of `split`. – Wiktor Stribiżew Oct 19 '19 at 09:24

Emma · Answer 2 · 2019-10-19T05:04:08.683

Maybe,

<tag>.*?<\/tag>|[^<>]+

would work OK:

Test

function regularExpression(regex, str) {
 let m, arr = [];
 while ((m = regex.exec(str)) !== null) {
  // This is necessary to avoid infinite loops with zero-width matches
  if (m.index === regex.lastIndex) {
   regex.lastIndex++;
  }


  m.forEach((match, groupIndex) => {
   arr.push(match.trim());
   console.log(`Found match, group ${groupIndex}: ${match}`);
  });
 }
 return arr;
}

const expression = /<tag>.*?<\/tag>|[^<>]+/g;
const string = 'The quick brown <tag>fox</tag> jumps over the lazy <tag>dog</tag>';

console.log(regularExpression(expression, string));

If you wish to simplify/modify/explore the expression, it's been explained on the top right panel of regex101.com. If you'd like, you can also watch in this link, how it would match against some sample inputs.

RegEx Circuit

jex.im visualizes regular expressions:

I tried this and it works but I feel the first answer is simpler and enough for the implementation requirements. Thanks for providing visualization! — webedward, Oct 22 '19 at 17:48

JS Regex lookbehind not working in firefox and safari

2 Answers2

Test

RegEx Circuit

Linked