use-isnan.md

Pattern: Direct comparison with NaN

Issue: -

Description

In JavaScript, NaN is not equal to itself or any other value, making direct comparisons with NaN always return false. Use Number.isNaN() or the global isNaN() function to properly check for NaN values.

Examples

Example of incorrect code:

if (foo == NaN) {
  // always false
}

if (foo === NaN) {
  // always false
}

if (foo != NaN) {
  // always true
}

if (value >= NaN) {
  // always false
}

Example of correct code:

if (Number.isNaN(foo)) {
  // proper check
}

if (isNaN(value)) {
  // global function works too
}

// Or check the type
if (typeof foo === 'number' && isNaN(foo)) {
  // more precise check
}