canisoon

Lookbehind in JS regular expressions

76.23

JS

The positive lookbehind (`(?<= )`) and negative lookbehind (`(?<! )`) zero-width assertions in JavaScript regular expressions can be used to ensure a pattern is preceded by another pattern.

Further reading:

  1. Can I use page for: Lookbehind in JS regular expressions
  2. Blog post on lookbehind assertions
  3. Firefox implementation bug
  4. MDN: Regular Expressions Assertions
  5. Safari implementation bug