Boolean

The Boolean object is an object wrapper for a boolean value.

Syntax

new Boolean([value])

Parameters

value

Optional. The initial value of the Boolean object.

Description

The value passed as the first parameter is converted to a boolean value, if necessary. If the value is omitted or is 0, -0, null, false, NaN, undefined, or the empty string (""), the object has an initial value of false. If the DOM object document.all is passed as a parameter, the new boolean object also has an initial value of false. All other values, including any object or the string "false", create an object with an initial value of true.

Do not confuse the primitive Boolean values true and false with the true and false values of the Boolean object.

Any object of which the value is not undefined or null, including a Boolean object whose value is false, evaluates to true when passed to a conditional statement. For example, the condition in the following if statement evaluates to true:

var x = new Boolean(false);
if (x) {
  // this code is executed
}

This behavior does not apply to Boolean primitives. For example, the condition in the following if statement evaluates to false:

var x = false;
if (x) {
  // this code is not executed
}

Do not use a Boolean object to convert a non-boolean value to a boolean value. Instead, use Boolean as a function to perform this task:

var x = Boolean(expression);     // preferred
var x = new Boolean(expression); // don't use

If you specify any object, including a Boolean object whose value is false, as the initial value of a Boolean object, the new Boolean object has a value of true.

var myFalse = new Boolean(false);   // initial value of false
var g = Boolean(myFalse);       // initial value of true
var myString = new String('Hello'); // string object
var s = Boolean(myString);      // initial value of true

Do not use a Boolean object in place of a Boolean primitive.

Properties

Boolean.length

Length property whose value is 1.

Boolean.prototype

Represents the prototype for the Boolean constructor.

Methods

While the global Boolean object contains no methods of its own, it does inherit some methods through the prototype chain:

Boolean instances

All Boolean instances inherit from Boolean.prototype. As with all constructors, the prototype object dictates instances' inherited properties and methods.

Properties

Boolean.prototype.constructor

Returns the function that created an instance's prototype. This is the Boolean function by default.

Methods

Boolean.prototype.toSource()

Returns a string containing the source of the Boolean object; you can use this string to create an equivalent object. Overrides the Object.prototype.toSource() method.

Boolean.prototype.toString()

Returns a string of either "true" or "false" depending upon the value of the object. Overrides the Object.prototype.toString() method.

Boolean.prototype.valueOf()

Returns the primitive value of the Boolean object. Overrides the Object.prototype.valueOf() method.

Examples

Creating Boolean objects with an initial value of false

var bNoParam = Boolean();
var bZero = Boolean(0);
var bNull = Boolean(null);
var bEmptyString = Boolean('');
var bfalse = Boolean(false);

Creating Boolean objects with an initial value of true

var btrue = Boolean(true);
var btrueString = Boolean('true');
var bfalseString = Boolean('false');
var bSuLin = Boolean('Su Lin');
var bArrayProto = Boolean([]);
var bObjProto = Boolean({});

Specifications

Browser compatibility

See also

• Boolean.prototype
• Boolean
• Boolean data type (Wikipedia)