Pattern: Optional assertion that serves no purpose
Issue: -
Assertions that are quantified (directly or indirectly) can be considered optional if the quantifier has a minimum of zero.
A simple example is the following pattern: /a(?:$)*b/. The $ assertion will reject, but if that happens it will simply be ignored because of the * quantifier. The assertion is optional, serving no function whatsoever.
More generally, an assertion is optional, if there exists a parent quantifier with a minimum of zero such that all possible paths of the quantified element that contain the assertion do not consume characters.
/* eslint regexp/no-optional-assertion: "error" */
/* ✓ GOOD */
var foo = /\w+(?::|\b)/;
/* ✗ BAD */
var foo = /a(?:$)*b/;
var foo = /a(?:foo|(?<!-)(?:-|\b))*b/; // The \b is optional
var foo = /(?:^)?\w+/; // warns about ^
var foo = /\w+(?::|$)?/; // warns about $