undefinedTypeofChecks

Reports typeof undefined checks.

✅ This rule is included in the ts stylistic presets.

Using typeof x === "undefined" is verbose and can be simplified to x === undefined. Direct comparisons are clearer and more concise.

Examples

❌ Incorrect

if (typeof value === "undefined") {
  // handle undefined
}

if (typeof value !== "undefined") {
  // value is defined
}

✅ Correct

if (value === undefined) {
  // handle undefined
}

if (value !== undefined) {
  // value is defined
}

Options

This rule is not configurable.

When Not To Use It

In rare cases where you need to check for undefined in a global scope where undefined might be shadowed, typeof checks are safer. However, in modern JavaScript, this is very uncommon.

Further Reading

• MDN: undefined
• MDN: typeof

Equivalents in Other Linters

• ESLint: unicorn/no-typeof-undefined
• Oxlint: unicorn/no-typeof-undefined