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    NaN

    The global NaN property is a value representing Not-A-Number.

    Property attributes of NaN
    Writable no
    Enumerable no
    Configurable no

    Syntax

    NaN

    Description

    NaN is a property of the global object.

    The initial value of NaN is Not-A-Number — the same as the value of Number.NaN. In modern browsers, NaN is a non-configurable, non-writable property. Even when this is not the case, avoid overriding it.

    It is rather rare to use NaN in a program. It is the returned value when Math functions fail (Math.sqrt(-1)) or when a function trying to parse a number fails (parseInt("blabla")).

    Testing against NaN

    NaN compares unequal (via ==, !=, ===, and !==) to any other value -- including to another NaN value.  Use Number.isNaN() or isNaN() to most clearly determine whether a value is NaN.  Or perform a self-comparison: NaN, and only NaN, will compare unequal to itself.

    NaN === NaN;        // false
    Number.NaN === NaN; // false
    isNaN(NaN);         // true
    isNaN(Number.NaN);  // true
    
    function valueIsNaN(v) { return v !== v; }
    valueIsNaN(1);          // false
    valueIsNaN(NaN);        // true
    valueIsNaN(Number.NaN); // true
    

    Specifications

    Specification Status Comment
    ECMAScript 1st Edition. Standard Initial definition. Implemented in JavaScript 1.3
    ECMAScript 5.1 (ECMA-262)
    The definition of 'NaN' in that specification.
    Standard  
    ECMAScript 2015 (6th Edition, ECMA-262)
    The definition of 'NaN' in that specification.
    Standard  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

    See also

    Document Tags and Contributors

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    Last updated by: teoli,
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