Support logical assignments

Logical assignment proposal is now Stage 4.

https://github.com/tc39/proposal-logical-assignment

ESLint’s default parser will support this syntax under ecmaVersion: 2021

• ESTree: https://github.com/estree/estree/pull/233
• Acorn: https://github.com/acornjs/acorn/pull/968
• Espree: https://github.com/eslint/espree/pull/448
• ESLint:
  • Code path analysis #13612
  • operator-assignment #13618
  • constructor-super #13618
  • astUtils.couldBeError #13618
  • no-constant-condition #13946
  • complexity #13979
  • func-names #14908
  • no-self-assign? #14152

[mdjermanovic]

ESLint also supports logical assignment operators, as of v7.8.0.

If you’re using the default parser, just update the ecmaVersion to the latest 2021:

"parserOptions": {
   "ecmaVersion": 2021
}

The core and most of the rules have been updated in v7.8.0.

We left this issue open for changes that were considered to be breaking for babel-eslint users, and those changes will be implemented in ESLint v8. There are also some minor changes that were blocked at the moment, we’ll implement them in some of the future v7 minor releases.

[mdjermanovic]

var foo ||= bar;

@aduh95 this isn’t valid VariableStatement, ||= bar cannot be Initializer. This code is syntax error in engines, too.