NaN is a JavaScript reserved word indicating that a number is not a legal number.
Trying to do arithmetic with a non-numeric string will result in NaN (Not a Number):
Example
var x = 100 / "Apple"; // x will be NaN (Not a Number)
However, if the string contains a numeric value , the result will be a number:
Example
var x = 100 / "10"; // x will be 10
You can use the global JavaScript function isNaN() to find out if a value is a number:
Example
var x = 100 / "Apple";
isNaN(x); // returns true because x is Not a Number
isNaN(x); // returns true because x is Not a Number
Watch out for NaN. If you use NaN in a mathematical operation, the result will also be NaN:
Example
var x = NaN;
var y = 5;
var z = x + y; // z will be NaN
var y = 5;
var z = x + y; // z will be NaN
Or the result might be a concatenation:
Example
var x = NaN;
var y = "5";
var z = x + y; // z will be NaN5
var y = "5";
var z = x + y; // z will be NaN5
NaN is a number: typeof NaN returns number:
Example
typeof NaN; // returns "number"
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