JavaScript NumberObject

JavaScript has only one type of number.

Numbers can be written with or without a decimal point.

JavaScript Numbers

JavaScript numbers can be written with or without a decimal point:

Examples

var pi=3.14; // Uses a decimal point
var x=34; // Does not use a decimal point

Very large or very small numbers can be written using scientific (exponential) notation:

Examples

var y=123e5;    // 12300000
var z=123e-5;   // 0.00123

All JavaScript numbers are 64-bit

JavaScript is not a typed language. Unlike many other programming languages, JavaScript does not define different types of numbers, such as integers, short, long, floating-point, and so on.

In JavaScript, numbers are not divided into integer and floating-point types; all numbers are of the floating-point type. JavaScript uses the 64-bit floating-point format defined by the IEEE754 standard to represent numbers. It can represent a maximum value (Number.MAX_VALUE) of±1.7976931348623157e+308, and a minimum value (Number.MIN_VALUE) of±5e-324。

This format uses 64 bits to store numeric values, where bits 0 to 51 store the number (fraction), bits 52 to 62 store the exponent, and bit 63 stores the sign:

Value (aka Fraction/Mantissa) Exponent Sign
52 bits (0 - 51)  11 bits (52 - 62) 1 bit (63)


Precision

Integers (without a decimal point or exponent notation) can have up to 15 digits.

Examples

var x = 999999999999999; //x is 999999999999999 var y = 9999999999999999; //y is 10000000000000000

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The maximum number of decimal places is 17, but floating-point arithmetic is not always 100% accurate:

Examples

var x = 0.2+0.1; // The output is 0.30000000000000004

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Octal and Hexadecimal

If the prefix is 0, JavaScript interprets the numeric constant as an octal number; if the prefix is 0 and "x", it interprets it as a hexadecimal number.

Examples

var y = 0377;
var z = 0xFF;

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lamp Never write a zero before a number, unless you need an octal conversion.

By default, JavaScript numbers are displayed in decimal.

But you can use the toString() method to output hexadecimal, octal, and binary.

Examples

var myNumber=128;
myNumber.toString(16); // Returns 80
myNumber.toString(8); // Returns 200
myNumber.toString(2); // Returns 10000000

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Infinity

When a numeric operation exceeds the upper limit of numbers that JavaScript can represent (overflow), the result is a special infinity value, represented as Infinity in JavaScript. Similarly, when a negative number exceeds the range of negative numbers that JavaScript can represent, the result is negative infinity, represented as -Infinity in JavaScript. The behavior of infinity values is consistent with what we expect: the results of addition, subtraction, multiplication, and division based on them are still infinity (of course retaining their signs).

Examples

myNumber=2;
while (myNumber!=Infinity)
{
myNumber=myNumber*myNumber; // Repeat the calculation until myNumber equals Infinity
}

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Dividing by 0 also produces infinity:

Examples

var x = 2/0;
var y = -2/0;

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NaN - Non-numeric Value

The NaN property is a special value representing a non-numeric value. This property is used to indicate that a value is not a number. You can set a Number object to this value to indicate that it is not a numeric value.

You can use the isNaN() global function to determine whether a value is a NaN value.

Examples

var x = 1000 / "Apple";
isNaN(x); // Returns true
var y = 100 / "1000";
isNaN(y); // Returns false

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Dividing by 0 gives infinity, and infinity is a number:

Examples

var x = 1000 / 0;
isNaN(x); // Returns false

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Numbers can be numbers or objects

Numbers can be initialized with primitive data, like x = 123;

JavaScript Number objects are initialized with data, var y = new Number(123);

Examples

var x = 123;
var y = new Number(123);
typeof(x) // Returns Number
typeof(y) // Returns Object

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Examples

var x = 123;             
var y = new Number(123);
(x === y) // is false, because x is a number and y is an object

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Number Properties

Property Description
Number.MAX_VALUE Maximum value
Number.MIN_VALUE Minimum value
Number.NaN Non-numeric
Number.NEGATIVE_INFINITY Negative infinity, returned on overflow
Number.POSITIVE_INFINITY Positive infinity, returned on overflow
Number.EPSILON

Represents the difference between 1 and the smallest Number greater than 1 and closest to 1.
Number.MIN_SAFE_INTEGER Minimum safe integer.
Number.MAX_SAFE_INTEGER Maximum safe integer.

Number Methods

Method Description
Number.parseFloat() Converts a string to a floating-point number. Same as the global methodparseFloat()in effect.
Number.parseInt()

Converts a string to an integer. Same as the global methodparseInt()in effect.
Number.isFinite() Determines whether the passed parameter is a finite number.
Number.isInteger() Determines whether the passed parameter is an integer.
Number.isNaN() Determines whether the passed parameter is NaN.
Number.isSafeInteger() Determines whether the passed parameter is a safe integer.

Some methods on the number type prototype

Method Description
toExponential() Returns a string of a number in exponential notation, e.g.: 1.23e+2
toFixed()

Returns a representation with the specified number of decimal places.

var a=123;
b=a.toFixed(2); // b="123.00"
toPrecision()

Returns a number with the specified precision. In the example below, in a=123, the 3 will disappear due to precision limitations:

var a=123;
b=a.toPrecision(2); // b="1.2e+2"
Other extensions