no-shadow-restricted-names

undefined, NaN and Infinity look like keywords, but they're ordinary globals, so a variable or a parameter can take their name. After const undefined = "none", every value === undefined in that scope compares with "none".

The rule reports variables, parameters, functions, classes and imports with one of these names.

This rule is on by default.

Configure

On by default as a warning. To turn it off:

[lint.rules]
"no-shadow-restricted-names" = "off" # or "error"

Every option, set to its default:

[lint.rules]
"no-shadow-restricted-names" = ["warn", {
  reportGlobalThis = true,
}]

Examples

Reported:

const undefined = "none";

function toNumber(text, NaN) {
  return text === "" ? NaN : Number(text);
}

Not reported:

const missing = "none";

function toNumber(text, fallback) {
  return text === "" ? fallback : Number(text);
}

A variable named undefined that never gets a value is allowed, because it's the same as the global:

var undefined;

Options

Option	Default	What it does
reportGlobalThis	true	Also report globalThis.

If your project has an ESLint config and ESLint 9 or older installed, the default is false, as it is there.

const globalThis = window;

const globalThis = window;