Javascript Double Not Operator

Learn when we use Javascript Double Not or not not Operator

Published March 10, 2020

Javascript Double Not Operator

Javascript Double Not Operator

It converts a nonboolean to an inverted boolean.

For Example, !8 will be false, since 8 is a non-false value in Javascript.

However, If you boolean-inverts that 8 like !!8 then you will get the original value as a boolean which is true.


!8   //false
!!8  //true

More Examples

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

              !!0 === false
!!parseInt("foo") === false // NaN is falsy
              !!1 === true
             !!-1 === true  // -1 is truthy

             !!"" === false // empty string is falsy
          !!"foo" === true  // non-empty string is truthy
        !!"false" === true  // ...even if it contains a falsy value

     !!window.foo === false // undefined is falsy
           !!null === false // null is falsy

             !!{} === true  // an (empty) object is truthy
             !![] === true  // an (empty) array is truthy; PHP programmers beware!