group capturing multiple times behind stable prefix

Question

Is it possible to create a regex that retrieves all capturing groups matching that type of html input:

<em>word1</em> <em>word2</em> <em>word3</em>
prefix: <em>word4</em> <em>word5</em>
<em>word6</em> <em>word7</em>

That matches

word4 word5

I have tried with Lookahead and Lookbehind Zero-Length Assertions but with no success.

Here is my try

https://regex101.com/r/lA9xA3/2

But I do know how to make groups repeating on every next occurence following my 'prefix: '

Thanks a lot,

Julien

JS regex engine does not support lookbehind. Using [capturing mechanism](https://regex101.com/r/yK7vC3/1) is a traditional workaround. — Wiktor Stribiżew, Jan 27 '16 at 21:18
Ok, I have tried the following (?:)(\w*\d*)(?:<\/em>) but I do not want the noise around, just the matching ones following 'prefix:' string — darul75, Jan 27 '16 at 21:20
Yes but I would like to extract all content of tags when 'prefix:' string is present before it. — darul75, Jan 27 '16 at 21:26
So, what is so difficult here? [This](https://jsfiddle.net/nyzuh8ed/)? — Wiktor Stribiżew, Jan 27 '16 at 21:29
my comments here, https://jsfiddle.net/darul75/w5auqmht/1/ I will check tomorrow how to make it different if not a duplicate. thanks — darul75, Jan 27 '16 at 21:35
Ok, I get the point, but please edit the question with the description of the real problem. — Wiktor Stribiżew, Jan 27 '16 at 21:37
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/101823/discussion-between-darul75-and-wiktor-stribizew). — darul75, Jan 27 '16 at 21:39
I think you can use [this demo](https://jsfiddle.net/7papk7ko/). Please check and let me know. — Wiktor Stribiżew, Jan 27 '16 at 21:57
This solution works very well. I thought it could be possible to avoid 2 regexps but it meets my needs , thank you. — darul75, Jan 28 '16 at 08:58

score 1 · Accepted Answer · answered Jan 28 '16 at 09:13

You need to get the line that begins with the prefix and then get the texts inside <em> tags.

This is better done in two passes in order not to compromise performance and readability:

var re = /^prefix:((?: *<em>\w*\d*<\/em>)*) */gm; 
var str = 'prefix: <em>word1</em> <em>word2</em> <em>word3</em>\n<em>word4</em> <em>word5</em>\nprefix: <em>word6</em> <em>word7</em> <em>word8</em>';
var arr = [];
 
while ((m = re.exec(str)) !== null) {
  var tmp = m[1].match(/[^<>]*(?=<\/em)/g); // Get matches inside EM
  if (tmp) {                                // If there are any
    tmp = tmp.filter(Boolean);              // Remove empty array elements
    for (var i=0; i<tmp.length;i++) {
      arr.push(tmp[i]);                     // Add to resulting array
    }
  }
}
document.body.innerHTML = "<pre>" + JSON.stringify(arr, 0, 4) + "</pre>";

group capturing multiple times behind stable prefix

1 Answers1