为什么 ESLint 没有检测到更高版本 ES 的全局变量？

Question

index.js:

var mySet = new Set();

Command:

npx eslint --no-eslintrc index.js

Problem: ESLint doesn't detect that Set doesn't exist in ES5.

However, ESLint explains ( https://eslint.org/docs/latest/user-guide/configuring/language-options#specifying-parser-options ):

By default, ESLint expects ECMAScript 5 syntax.

And for the env property, that provides global variables ( https://eslint.org/docs/latest/user-guide/configuring/language-options#specifying-environments ):

es6 - enable all ECMAScript 6 features except for modules (this automatically sets the ecmaVersion parser option to 6).

for new ES6 global variables, use { "env": { "es6": true } }

Do you know why ESLint doesn't trigger any error for new Set() ? The problem remains the same if I use an eslintrc with env and parserOptions empty, or "ecmaVersion": 5 for parserOptions .

Answer 1

The problem was that, as Bergi said, ESLint did not complain about undefined variables .

Example:

var s = new Set();
var f = new Foo(); // (Foo does not exist)

-> ESLint does not complain.

However, if I add "extends": "eslint:recommended" to my eslintrc, then both lines fail, because of https://eslint.org/docs/latest/rules/no-undef .

Indeed, if I add:

{ "env": { "es6": true } }

to my eslintrc, then var f = new Foo(); fails, but var s = new Set(); does not.