ESLint v9.31.0 released

Highlights

Explicit resource management support in core rules

Four core rules have been updated to better support explicit resource management, a new feature in ES2026 JavaScript, including support for using and await using syntax.

The init-declarations rule no longer reports on initializing using and await using variables when the option is "never", because these variables must be initialized. For example:

async function foobar() {
 await using quux = getSomething();
}

The no-const-assign rule now reports on modifying using and await using variables. For example:

if (foo) {
 using a = getSomething();
 a = somethingElse;
}

The no-loop-func rule no longer reports on references to using and await using variables, because these variables are constant. For example:

for (using i of foo) {
    var a = function() { return i; }; // OK, all references are referring to block scoped variables in the loop.
    a();
}

The no-undef-init rule no longer reports on using and await using variables initialized to undefined. For example:

using foo = undefined;

Improved RuleTester output for incorrect locations

The run method of the RuleTester class has been enhanced to indicate when multiple properties of a reported error location in a test case do not match. For example:

      AssertionError [ERR_ASSERTION]: Actual error location does not match expected error location.
+ actual - expected

  {
+   column: 31,
+   endColumn: 32
-   column: 32,
-   endColumn: 33
  }

Previously, the output would only show one property even if there were multiple mismatches:

      AssertionError [ERR_ASSERTION]: Error column should be 32

31 !== 32

      + expected - actual

      -31
      +32

Features

• 35cf44c feat: output full actual location in rule tester if different (#19904) (ST-DDT)
• a6a6325 feat: support explicit resource management in no-loop-func (#19895) (Milos Djermanovic)
• 4682cdc feat: support explicit resource management in no-undef-init (#19894) (Milos Djermanovic)
• 5848216 feat: support explicit resource management in init-declarations (#19893) (Milos Djermanovic)
• bb370b8 feat: support explicit resource management in no-const-assign (#19892) (Milos Djermanovic)

Bug Fixes

• 07fac6c fix: retry on EMFILE when writing autofix results (#19926) (TKDev7)
• 28cc7ab fix: Remove incorrect RuleContext types (#19910) (Nicholas C. Zakas)

Documentation

• 664cb44 docs: Update README (GitHub Actions Bot)
• 40dbe2a docs: fix mismatch between globalIgnores() code and text (#19914) (MaoShizhong)
• 5a0069d docs: Update README (GitHub Actions Bot)
• fef04b5 docs: Update working on issues info (#19902) (Nicholas C. Zakas)

Chores

• 3ddd454 chore: upgrade to @eslint/js@9.31.0 (#19935) (Francesco Trotta)
• d5054e5 chore: package.json update for @eslint/js release (Jenkins)
• 0f4a378 chore: update eslint (#19933) (renovate[bot])
• 76c2340 chore: bump mocha to v11 (#19917) (루밀LuMir)