Dive Into JavaScript

The JavaScript Number Object

The number data type is a primitive data type that can hold numeric values such as integers and floating-point numbers.

A number primitive can be declared using the literal notation:

var num_int = 42;
var num_float = 1.61803399;

All numbers in JavaScript are 64-bit floating point numbers. JavaScript does not distinguish between integers and floating point numbers.

Integers can also be specified in octal (base 8) or hexadecimal (base 16) notation. To use the octal notation, numbers must be preceeded with a 0:

var num_oct = 052; // equivalent to 42 decimal

To use the hexadecimal notation, numbers must be preceeded with 0x:

var num_hex = 0x2a; // equivalent to 42 decimal

The JavaScript Number object represents a wrapper for the number primitive. A Number object can be created using the new Number() object constructor:

var num1 = new Number(value)

The value parameter represents the numeric value of the object. For example, the following code will create a Number object with a value of 7:

var num2 = new Number(7);

Calling the constructor without a parameter creates an object with an initial value of 0.

The global function Number() can be called without the new keyword to create a number primitive. For example:

var num3 = Number(3); // returns the primitive value 3

The Number() global function can also be used to explicitly convert a value to a number:

var num4 = Number("123");

For a value that can not be converted to a number, the Number() function returns the special value NaN (Not-a-Number) which indicates that the expression could not be evaluated to a number. For example, converting arrays and objects to numbers is not possible, thus the function will return NaN:

Number([1, 2, 3]); // returns NaN

Only basic types such as strings and boolean values can be converted to numbers. Note, however, that a string can be converted to a number only if it is a numeric string:

Number("123"); // 123
Number("foo"); // NaN
Number("123foo"); // NaN

Number Properties

constructor

Returns a reference to the function that created the Number object

MAX_VALUE

Represents the largest representable number

MIN_VALUE

Represents the smallest representable number

NaN

NaN is a special value indicating that the value is "Not-a-Number"

NEGATIVE_INFINITY

Represents negative infinity

POSITIVE_INFINITY

Represents positive infinity

prototype

Allows the addition of properties and methods to all objects

Number Methods

toExponential([digits])

Returns a string representing the Number object in exponential notation, also known as scientific notation

toFixed([digits])

Returns a string representing the Number object formatted using fixed-point notation

toLocaleString()

Returns a locale-aware string representation of the Number object

toPrecision([precision])

Returns a string representing the Number object to the specified precision

toString([radix])

Returns a string representation of the Number object in the specified radix or base

valueOf()

Returns the primitive value of the number

See also

• The NaN property
• The isNaN() function
• The parseFloat() function
• The parseInt() function