RegExp lookbehind assertions

Lookarounds are zero-width assertions that match a string without consuming anything. ECMAScript has lookahead assertions that does this in forward direction, but the language is missing a way to do this backward which the lookbehind assertions provide. With lookbehind assertions, one can make sure that a pattern is or isn't preceded by another, e.g. matching a dollar amount without capturing the dollar sign.

Documentation

• https://mathiasbynens.be/notes/es-regexp-proposals#lookbehinds
• https://developers.google.com/web/updates/2017/07/upcoming-regexp-features#lookbehind_assertions

Specification

Working draft or equivalent

Status in Chromium

Blink components: Blink>JavaScript>Language

Enabled by default (tracking bug) in:

• Chrome for desktop release 62
• Chrome for Android release 62
• Android WebView release 62
• Opera release 49
• Opera for Android release 49

Consensus & Standardization

• Firefox: No public signals
• Edge: Public support
• Safari: No public signals
• Web Developers: Strongly positive

Owners

• mathias@chromium.org
• littledan@chromium.org
• yangguo@chromium.org
• erikcorry@chromium.org

Last updated on 2017-08-10