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Disallow unsupported ECMAScript syntax on the specified version (n/no-unsupported-features/es-syntax)

💼 This rule is enabled in the ✅ recommended config.

ECMAScript standard is updating every two months. You can check node.green to know which Node.js version supports each ECMAScript feature.

This rule reports unsupported ECMAScript syntax on the configured Node.js version as lint errors. Editor integrations of ESLint would be useful to know it in real-time.

📖 Rule Details

Supported ECMAScript features

This rule supports ECMAScript 2019 and proposals that have been approved as Stage 4 by August 2019. See also TC39 finished proposals.

Please configure your .eslintrc file to succeed to succeed in parsing the syntax. For example, set 2020 to parserOptions.ecmaVersion.

Configured Node.js version range

This rule gets the supported Node.js version range from the following, falling back to the next if unspecified:

  1. Rule configuration version
  2. ESLint shared setting node.version
  3. package.json engines field
  4. >=16.0.0

If you omit the [engines] field, this rule chooses >=16.0.0 as the configured Node.js version since 16 is the active lts (see also Node.js Release Working Group).

For Node.js packages, using the engines field is recommended because it's the official way to indicate support:

{
    "name": "your-module",
    "version": "1.0.0",
    "engines": {
        "node": ">=16.0.0"
    }
}

For Shareable Configs or packages with a different development environment (e.g. pre-compiled, web package, etc.), you can configure ESLint with settings.node.version to specify support.

Options

{
    "n/no-unsupported-features/es-syntax": ["error", {
        "version": ">=16.0.0",
        "ignores": []
    }]
}

version

As mentioned above, this rule reads the engines field of package.json. But, you can overwrite the version by version option.

The version option accepts the valid version range of node-semver.

ignores

If you are using transpilers, maybe you want to ignore the warnings about some features. You can use this ignores option to ignore the given features.

The "ignores" option accepts an array of the following strings.

ES2020:

  • "bigint"
  • "dynamicImport"
  • "optionalChaining"
  • "nullishCoalescingOperators"

ES2019:

  • "jsonSuperset"
  • "optionalCatchBinding"

ES2018:

  • "asyncIteration"
  • "malformedTemplateLiterals"
  • "regexpLookbehind"
  • "regexpNamedCaptureGroups"
  • "regexpS"
  • "regexpUnicodeProperties"
  • "restSpreadProperties"

ES2017:

  • "asyncFunctions"
  • "trailingCommasInFunctions"

ES2016:

  • "exponentialOperators"

ES2015:

  • "arrowFunctions"
  • "binaryNumericLiterals"
  • "blockScopedFunctions"
  • "blockScopedVariables"
  • "classes"
  • "computedProperties"
  • "defaultParameters"
  • "destructuring"
  • "forOfLoops"
  • "generators"
  • "modules"
  • "new.target"
  • "objectSuperProperties"
  • "octalNumericLiterals"
  • "propertyShorthands"
  • "regexpU"
  • "regexpY"
  • "restParameters"
  • "spreadElements"
  • "templateLiterals"
  • "unicodeCodePointEscapes"

Shared Settings

The following options can be set by shared settings. Several rules have the same option, but we can set this option at once.

  • version

For Example:

{
    "settings": {
        "node": {
            "version": ">=16.0.0",
        }
    },
    "rules": {
        "n/no-unsupported-features/es-syntax": ["error", {
            "ignores": []
        }]
    }
}

🔎 Implementation