Meaning of !! javascript

 

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  • What is the !! (not not) operator in JavaScript? 31 answers

    • !! Converts any value to a boolean value 

     > !!null
 false

 > !!true
 true

 > !!{}
 true

 > !!false
 false

    If a value is falsey then the result will be false . If it is truthy the result will be true .

    Even more, the third ! inverts the converted value so the above examples become: 

        > !!!null
    true

    > !!!true
    false

    > !!!{}
    false

    > !!!false
    true

    It forces what is returned to be a boolean and not an integer or empty value. For example, 0 evaluates to false with == but will not with === . So to be sure that any integer 0 returned will be converted into an boolean, we use !! . This also works if null or undefined is returned.

    So whats happening is actually: 

    var test = null;
var result = !test; // returns true
    result = !return; // returns false

    !! is used to convert the value to the right of it to its equivalent boolean value. 

    !!false === false
!!true === true
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