n/no-unsupported-features/es-syntax

Syntax that's newer than the oldest Node.js you support is a SyntaxError there, so the file doesn't load at all. You only find out when somebody runs it on that version.

The rule takes the versions you support from engines.node in your package.json. If nothing sets a range, it assumes >=16.0.0. Every version in the range must have the feature.

Besides syntax, it reports newer built-ins such as Object.hasOwn, and newer methods such as .at() when the code shows they're called on an array or a string.

Configure

Off by default. To turn it on:

[lint.rules]
"n/no-unsupported-features/es-syntax" = "error" # or "warn"

Every option, set to its default. The ones that are commented out are unset by default.

[lint.rules]
"n/no-unsupported-features/es-syntax" = ["error", {
  # version = <string>,
  ignores = [], # list of strings
}]

Examples

Reported, because Node.js has had static blocks since 16.11.0 and the v flag since 20.0.0:

class Cache {
  static instance;
  static {
    Cache.instance = new Cache();
  }
}

const word = /[\p{L}--[a-z]]/v;

Not reported:

class Cache {
  static instance = new Cache();
}

const word = /\p{L}/u;

With a newer engines.node, static blocks are fine:

{
  "name": "app",
  "engines": { "node": ">=18.0.0" }
}

class Cache {
  static instance;
  static {
    Cache.instance = new Cache();
  }
}

A method is reported if the rule can tell that the value is an array or a string:

const steps = ["build", "test", "publish"];
const last = steps.at(-1);

function lastOf(steps) {
  return steps.at(-1);
}

Options

Option	Default	What it does
version	engines.node, or ">=16.0.0"	The range of Node.js versions you support, written as in package.json.
ignores	[]	Features that are never reported, by the name in the message, such as "class-static-block".

Without version, the range comes from settings.n.version ([lint.settings.n] in bunfig.toml, or settings in an ESLint config), then from engines.node, then from devEngines.runtime in package.json.

[lint.rules]
"n/no-unsupported-features/es-syntax" = ["error", {
  version = ">=14.0.0",
  ignores = ["logical-assignment-operators"],
}]

options.retries ??= 3;

options.retries ??= 3;

options.retries ??= 3;

When not to use it

If you compile the code for the versions you target before it runs, with TypeScript or a bundler, the source can use any syntax.