Boolean Type

Description

The Boolean type is the reference type corresponding to the Boolean values.

To create a Boolean object, use the Boolean constructor and pass in either true or false.

Methods

Boolean reference type overrides the valueOf() method to return a primitive value of true or false.

The toString() method is overridden to return a string of "true" or "false".

Operation

var falseObject = new Boolean(false);
var result = falseObject && true;
console.log(result);  //true
//from  ww  w .ja  va2s. c om
var falseValue = false;
result = falseValue && true;
console.log(result);  //false

In this code, a Boolean object is created with a value of false. Then it is ANDed with the primitive value true. It should result to false. But it is the object named falseObject being evaluated, not its value ( false).

All objects are converted to true in Boolean expressions, so falseObject is given a value of true. Then, true ANDed with true is equal to true.

The code above generates the following result.

Note

The typeof operator returns "boolean" for the primitive but "object" for the reference.

A Boolean object is an instance of the Boolean type and will return true when used with the instanceof operator, whereas a primitive value returns false, as shown here:

var falseObject = new Boolean(false);
var falseValue = false;
/*from ww w .  j  a  v a2  s.  com*/
console.log(typeof falseObject);   //object
console.log(typeof falseValue);    //boolean
console.log(falseObject instanceof Boolean);  //true
console.log(falseValue instanceof Boolean);   //false

The code above generates the following result.