The Standard Library contains utilities that are functionally broken but remain for legacy reasons.

Number isNaN

Use Number.isNaN instead of global isNaN. The global isNaN coerces non-numbers to numbers, returning true for anything that coerces to NaN. If this behavior is desired, make it explicit.

ESLint: no-restricted-globals

Examples

⇣ Incorrect code for this rule:

isNaN("1.2"); // false
isNaN("1.2.3"); // true

⇡ Correct code for this rule:

Number.isNaN("1.2.3"); // false
Number.isNaN(Number("1.2.3")); // true

Number isFinite

Use Number.isFinite instead of global isFinite. The global isFinite coerces non-numbers to numbers, returning true for anything that coerces to a finite number. If this behavior is desired, make it explicit.

ESLint: no-restricted-globals

Examples

⇣ Incorrect code for this rule:

isFinite("2e3"); // true

⇡ Correct code for this rule:

Number.isFinite("2e3"); // false
Number.isFinite(parseInt("2e3", 10)); // true