are not numbers either:

js

    
    
    isNaN(NaN); // true
    isNaN(undefined); // true
    isNaN({}); // true
    
    isNaN(true); // false
    isNaN(null); // false
    isNaN(37); // false
    
    // Strings
    isNaN("37"); // false: "37" is converted to the number 37 which is not NaN
    isNaN("37.37"); // false: "37.37" is converted to the number 37.37 which is not NaN
    isNaN("37,5"); // true
    isNaN("123ABC"); // true: Number("123ABC") is NaN
    isNaN(""); // false: the empty string is converted to 0 which is not NaN
    isNaN(" "); // false: a string with spaces is converted to 0 which is not NaN
    
    // Dates
    isNaN(new Date()); // false; Date objects can be converted to a number (timestamp)
    isNaN(new Date().toString()); // true; the string representation of a Date object cannot be parsed as a number
    
    // Arrays
    isNaN([]); // false; the primitive representation is "", which coverts to the number 0
    isNaN([1]); // false; the primitive representation is "1"
    isNaN([1, 2]); // true; the primitive representation is "1,2", which cannot be parsed as number
    

##  Specifications

Specification  
---  
[ ECMAScript Language Specification  
#  sec-isnan-number  ](https://tc39.es/ecma262/multipage/global-
object.html#sec-isnan-number)  
  
##  Browser compatibility

BCD tables only load in the browser  with JavaScript enabled. Enable
JavaScript to view data.

##  See also

  * [ ` NaN ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN)
  * [ ` Number.isNaN() ` ](/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN)

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