JavaScript Booleans

The boolean (not Boolean) is a primitive data type in JavaScript. It can have only two values: true or false. It is useful in controlling program flow using conditional statements like if else, switch, while loop, etc.

The followings are boolean variables.

var YES = true;

var NO = false;

The following example demonstrates how a boolean value controls the program flow using the if condition.

var YES = true;
var NO = false;

if(YES)
{
    alert("This code block will be executed");
}

if(NO)
{
    alert("This code block will not be executed");
}

The comparison expressions return boolean values to indicate whether the comparison is true or false. For example, the following expressions return boolean values.

var a = 10, b = 20;

var result = 1 > 2; // false

result = a < b; // true

result = a > b; // false

result = a + 20 &gt; b + 5; // true

Boolean Function

JavaScript provides the Boolean() function that converts other types to a boolean type. The value specified as the first parameter will be converted to a boolean value. The Boolean() will return true for any non-empty, non-zero, object, or array.

var a = 10, b = 20;

var b1 = Boolean('Hello'); // true

var b2 = Boolean('h'); // true

var b3 = Boolean(10); // true

var b4 = Boolean([]); // true

var b5 = Boolean(a + b); // true

If the first parameter is 0, -0, null, false, NaN, undefined, '' (empty string), or no parameter passed then the Boolean() function returns false.

var b1 = Boolean(''); // false

var b2 = Boolean(0); // false

var b3 = Boolean(null); // false

var a;
var b4 = Boolean(a); // false

The new operator with the Boolean() function returns a Boolean object.

var bool = new Boolean(true);

alert(bool); // true

Any boolean object, when passed in a conditional statement, will evaluate to true.

var bool = new Boolean(false);

if(bool){
    alert('This will be executed.');
}

Boolean vs boolean

The new Boolean() will return a Boolean object, whereas it returns a boolean without the new keyword. The boolean (lower case) is the primitive type, whereas Boolean (upper case) is an object in JavaScript. Use the typeof operator to check the types.

var b1 = new Boolean(true);
var b2 = true;

typeof b1; // object
typeof b2; // boolean

Boolean Methods

Primitive or Boolean object includes following methods.