Booleans

The boolean primitive is a logical data type with only two values: true and false.

Boolean object

All values in JavaScript are implicitly true or false. The Boolean object can be used to coerce a value to a true or false boolean, based on the implicit true or false state of that value:

Boolean( "A string literal" ); > true 

Values that result in false include 0, null, undefined, NaN, an empty string (""), an omitted value, and a false boolean. All other values result in true.

Boolean( NaN ); > false Boolean( -0 ); > false Boolean( 5 ); > true Boolean( "false" ); // the value `"false"` is a string, and therefore implicitly true. > true 

Avoid using the Boolean object as a constructor. It creates an object containing a boolean value, not the boolean primitive you might expect:

const falseBoolean = Boolean( 0 ); const falseObject = new Boolean( 0 ); console.log( falseBoolean ); > false console.log( falseObject ); > Boolean { false } falseObject.valueOf(); > false 

Because all objects are inherently truthy, the resulting boolean object always loosely evaluates to true, even if it contains a false value:

const falseBoolean = Boolean( 0 ); const falseObject = new Boolean( 0 ); console.log( falseBoolean == true ); > false console.log( falseObject == true ); > false console.log( !!falseObject ); > true 

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