Number.isNaN()

isNaN(number)

Returns: boolean · Added in vES6 · Updated March 13, 2026 · Number

number nan isnan

The Number.isNaN() method determines whether the passed value is NaN. Unlike the global isNaN() function, this method does not coerce its argument to a number, making it more reliable for type checking.

Syntax

Number.isNaN(value)

Parameters

Parameter	Type	Description
`value`	any	The value to check

Return Value

Returns true if the value is exactly NaN, false otherwise.

Examples

Basic Usage

Number.isNaN(NaN);        // true

Operations That Produce NaN

Number.isNaN(0/0);        // true (division of zero by zero)
Number.isNaN(0 * NaN);    // true (multiplication with NaN)
Number.isNaN(Math.sqrt(-1)); // true (square root of negative)
Number.isNaN(Number('hello')); // true (invalid number parsing)

Values That Are Not NaN

Number.isNaN(42);         // false
Number.isNaN('42');       // false (string, not NaN)
Number.isNaN(undefined);  // false
Number.isNaN(null);       // false
Number.isNaN({});         // false

Comparison: Number.isNaN() vs global isNaN()

The global isNaN() coerces its argument, causing unexpected results:

isNaN('hello');           // true (coerced to NaN)
Number.isNaN('hello');    // false (not the number NaN)

isNaN('42');              // true (coerced to NaN... wait, no: '42' becomes 42!)
Number.isNaN('42');       // false

isNaN(undefined);        // true (coerced to NaN)
Number.isNaN(undefined); // false

Practical Example: Safe Division

function safeDivide(a, b) {
  if (b === 0) {
    return NaN;
  }
  const result = a / b;
  return Number.isNaN(result) ? NaN : result;
}

safeDivide(10, 2);    // 5
safeDivide(10, 0);    // NaN
safeDivide(0, 0);     // NaN

Practical Example: Calculator Results

When building a calculator, you need to handle NaN results gracefully:

function calculate(a, b, operator) {
  let result;
  switch (operator) {
    case '+': result = a + b; break;
    case '-': result = a - b; break;
    case '*': result = a * b; break;
    case '/': result = b !== 0 ? a / b : NaN; break;
    default: result = NaN;
  }
  
  if (Number.isNaN(result)) {
    return 'Invalid operation';
  }
  return result;
}

calculate(10, 5, '+');   // 15
calculate(10, 0, '/');   // "Invalid operation"
calculate(10, 5, '^');   // "Invalid operation"