shadowedRestrictedNames

Reports variable declarations that shadow JavaScript's restricted names.

✅ This rule is included in the ts untyped presets.

JavaScript provides a set of built-in global identifiers with well-known names. When you declare a variable, function, or class with one of these names, it “shadows” the global identifier and can cause unexpected behavior or make code harder to understand.

This rule reports shadowing of the most common global names that developers sometimes unintentionally shadow:

• arguments
• eval
• Infinity
• NaN
• undefined

Examples

❌ Incorrect

function processValue(undefined) {
  if (undefined === null) {
    return 0;
  }
  return undefined;
}

let NaN = 123;

class Infinity {
  value = 100;
}

✅ Correct

function processValue(value) {
  if (value === undefined) {
    return 0;
  }
  return value;
}

let notANumber = NaN;

class InfiniteValue {
  value = Infinity;
}

Options

This rule is not configurable.

When Not To Use It

If you are working in a large legacy project that came before modern practices, you might find that these names are too difficult to refactor away from. You might consider using Flint disable comments and/or configuration file disables for those specific situations instead of completely disabling this rule.

Further Reading

• MDN: arguments
• MDN: eval()
• MDN: Infinity
• MDN: NaN
• MDN: undefined

Equivalents in Other Linters

• Biome: noShadowRestrictedNames
• Deno: no-shadow-restricted-names
• ESLint: no-shadow-restricted-names
• Oxlint: eslint/no-shadow-restricted-names