| pageClass | sidebarDepth | title | description | since |
|---|---|---|---|---|
rule-details |
0 |
regexp/no-optional-assertion |
disallow optional assertions |
v0.9.0 |
💼 This rule is enabled in the ✅ plugin:regexp/recommended config.
disallow optional assertions
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.
Here's an example: a(?:foo|(?<!-)(?:-|\b))*b. The \b is optional. However, the lookbehind (?<!-) is not optional because the group (?:-|\b) right after it can consume a character.
Optional assertions don't affect the pattern in any way. They are essentially dead code.
/* 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 `$`Nothing.
This rule was taken from eslint-plugin-clean-regex.
This rule is compatible with clean-regex/no-optional-assertion rule.
This rule was introduced in eslint-plugin-regexp v0.9.0