If the certain The problem is that positive lookbehind feature may not be supported in all browser and we have to support IE 11. used if the next element to your match is as per requirement described Support could have been added to other browsers at any time, but this code would have continued choosing the inferior path. But browsers and standards are not perfect, and there are still some edge cases where detecting the browser is needed. There are five major rendering engines: Trident, Gecko, Presto, Blink, and WebKit. See atom/find-and … 1 Reply Last reply Reply Quote 0. Copy link thinkhy commented Apr 2, 2016. immediately followed by equal sign and then the element to look Positive lookbehind: (?<=Y)X, matches X, but only if there’s Y before it. But within the lookbehind itself, we enter a different little world. Would be a relief when implementing QSyntaxHighlighter ::highlightBlock(), at the present I need to make some awkward workarounds. Merged Lookbehind has no firefox support #3189. ddbeck merged 3 commits into mdn: master from … Restrictions: Most of the engines don't support various expressions inside Lookbehind . Watch 153 Star 2.8k Fork 1.2k Code. support - javascript regex positive lookbehind . Pull requests 37. ahead. They support full, variable-length lookbehind, which no regex engines I know of other than .NET and JGsoft (used by products like RegexBuddy) are capable of. # (*positive_lookbehind:pattern) A zero-width positive lookbehind assertion. If that particular element is present then the regex After reviewing all of the above better alternatives to user agent sniffing, there are still some potential cases where user agent sniffing is appropriate and justified. It is basically of two types. It is basically of two types. Never use the OS token to define if a browser is on mobile, tablet or desktop. (4) Here is a regex that works fine in most regex implementations: (?