Negative lookbehind for all `{{` not preceded by ``

Question

Given a string such as

The quick brown {{ fox }} jumped over the lazy <em>{{ dog }}</em>

I'm looking for a pattern that will match all instances of {{ not preceded by the  block

Whilst the pattern /(?<!>)\{{2}/gm will work, this is not an option for Firefox and IE flavours of JS.

I’ve done a fair bit of digging and can find a great deal of examples that almost get there but not quite. Getting a positive match for the string _>{{_ is no problem, but it’s the reverse of this that I’m looking for.

I feel like I might be heading in the wrong direction with a lookup approach like this. Am I missing something more simple here?

Granted - but the negative lookbehind captures the ones I want. However it wont work in IE and Firefox. — petehotchkiss, Jul 27 '18 at 13:25
What are you matching those strings for? Extracting or replacing? — Wiktor Stribiżew, Jul 27 '18 at 13:27
replacing - I want to run a replacement on the `{{` occurrences that are not preceded by a `` tag already — petehotchkiss, Jul 27 '18 at 13:28
Why not look ahead for the closing tag? `/{{[^}]*?}}(?!<\/em>)/g` — Joseph Marikle, Jul 27 '18 at 13:32
Possible duplicate of [Regex negative lookbehind not valid in JavaScript](https://stackoverflow.com/questions/35142364/regex-negative-lookbehind-not-valid-in-javascript) — Pierre Gourseaud, Jul 27 '18 at 13:43
@arius the question your linking to specifically asks WHY that example does not work in Plunker. I know why my example of a negative look behind doesn't work - I'm looking to secure possible examples of how I might approach my quandary from another angle. — petehotchkiss, Jul 27 '18 at 13:52
@JosephMarikle That's a really good idea. Gives me a direction to work with — petehotchkiss, Jul 27 '18 at 13:53
@petehotchkiss Doesn't the answer provided in the other thread answer your question ? — Pierre Gourseaud, Jul 27 '18 at 14:01
@Arius I'm afraid not - it's related - but the crux of the question is cognitively somewhat different. That is specifically asking "why" - I'm asking "how" I can take an alternative approach here. — petehotchkiss, Jul 27 '18 at 15:01

score 0 · Answer 1 · answered Jul 27 '18 at 13:29

0

I'm guessing you want to access whatever is inside those {{ }} and wrap it in a  tag.

You can use the RegEx ([^>]){{(.*?)}}

And replace with $1$2

([^>]) makes sure the preceding char isn't a >
{{(.*?)}} matches anything inside {{ }}

Demo.

answered Jul 27 '18 at 13:29

Zenoo

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That almost gets there - only slight snag in it is it will match the _e_ in `space{{ here }}` @Joseph Marikle's example above looks to have nailed it – petehotchkiss Jul 27 '18 at 13:58
@petehotchkiss It will, but it also replaces it back with `$1` – Zenoo Jul 27 '18 at 13:59

score 0 · Answer 2 · answered Jul 27 '18 at 13:36

You may match any  contents using [\s\S]*?<\/em> regex and then match the {{...}} substrings with {{[\s\S]*?}} pattern in all other contexts, capture either of them and use custom logic in the callback method:

console.log(
  "The quick brown {{ fox }} jumped over the lazy <em>{{ dog }}</em>"
          .replace(/<em>[\s\S]*?<\/em>|({{[\s\S]*?}})/g, function ($0,$1) {
                 return $1 ? '<em>' + $1 + '</em>' : $0;
            })
);

With $1 ?, we check if Group 1 matched, and if yes, the value is wrapped with  tags, else, it is just pasted back with $0 (the whole match).

score 0 · Accepted Answer · answered Jul 27 '18 at 13:37

You could instead look ahead for the closing tag: /{{[^}]*?}}(?!<\/em>)/g

let test = "The quick brown {{ fox }} jumped over the lazy <em>{{ dog }}</em> asdfafds {{ fox }} asdf asdf asdf sdfasdfsdf <em>{{ dog }}</em>";
console.log("input: " + test);
console.log("output: " + test.replace(/({{[^}]*?}})(?!<\/em>)/g, "<em>$1</em>"));

Negative lookbehind for all `{{` not preceded by ``

3 Answers3