JavaScript Number Methods

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JavaScript Number Methods

JavaScript provides a range of methods for handling and manipulating numbers. These methods allow you to format numbers, convert between different number representations, and validate numerical inputs. Understanding these methods is essential for effective numerical computations in web applications.

Number Methods and Properties

Primitive values (like 3.14 or 2014), cannot have properties and methods (because they are not objects).

But with JavaScript, methods and properties are also available to primitive values, because JavaScript treats primitive values as objects when executing methods and properties.

The toString() Method

The toString() method returns a number as a string.

All number methods can be used on any type of numbers (literals, variables, or expressions):

Example

var x = 123;
x.toString();            // returns 123 from variable x
(123).toString();        // returns 123 from literal 123
(100 + 23).toString();   // returns 123 from expression 100 + 23

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The toExponential() Method

toExponential() returns a string, with a number rounded and written using exponential notation.

A parameter defines the number of characters behind the decimal point:

Example

var x = 9.656;
x.toExponential(2);     // returns 9.66e+0
x.toExponential(4);     // returns 9.6560e+0
x.toExponential(6);     // returns 9.656000e+0

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The parameter is optional. If you don't specify it, JavaScript will not round the number.

The toFixed() Method

toFixed() returns a string, with the number written with a specified number of decimals:

Example

var x = 9.656;
x.toFixed(0);           // returns 10
x.toFixed(2);           // returns 9.66
x.toFixed(4);           // returns 9.6560
x.toFixed(6);           // returns 9.656000

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toFixed(2) is perfect for working with money.

The toPrecision() Method

toPrecision() returns a string, with a number written with a specified length:

Example

var x = 9.656;
x.toPrecision();        // returns 9.656
x.toPrecision(2);       // returns 9.7
x.toPrecision(4);       // returns 9.656
x.toPrecision(6);       // returns 9.65600

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The valueOf() Method

valueOf() returns a number as a number.

Example

var x = 123;
x.valueOf();            // returns 123 from variable x
(123).valueOf();        // returns 123 from literal 123
(100 + 23).valueOf();   // returns 123 from expression 100 + 23

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In JavaScript, a number can be a primitive value (typeof = number) or an object (typeof = object).

The valueOf() method is used internally in JavaScript to convert Number objects to primitive values.

There is no reason to use it in your code.

All JavaScript data types have a valueOf() and a toString() method.

This HTML document demonstrates how each of the number methods can be used in a practical web application. By running this code, you can see how these methods manipulate and interact with numerical values.

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Converting Variables To Numbers

Converting Variables to Numbers

There are 3 JavaScript methods that can be used to convert variables to numbers:

The Number() method
The parseInt() method
The parseFloat() method

These methods are not number methods, but global JavaScript methods.

Global JavaScript Methods

JavaScript global methods can be used on all JavaScript data types.

These are the most relevant methods, when working with numbers:

Method	Description
Number()	Returns a number, converted from its argument.
parseFloat()	Parses its argument and returns a floating point number
parseInt()	Parses its argument and returns an integer

The Number() Method

Number() can be used to convert JavaScript variables to numbers:

Example

Number(true);          // returns 1
Number(false);         // returns 0
Number("10");          // returns 10
Number(" 10");        // returns 10
Number("10 ");        // returns 10
Number(" 10 ");       // returns 10
Number("10.33");       // returns 10.33
Number("10,33");       // returns NaN
Number("10 33");       // returns NaN
Number("John");        // returns NaN

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If the number cannot be converted, NaN (Not a Number) is returned.

The Number() Method Used on Dates

Number() can also convert a date to a number:

Example

Number(new Date("2017-09-30")); // returns 1506729600000

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The Number() method above returns the number of milliseconds since 1.1.1970.

The parseInt() Method

parseInt() parses a string and returns a whole number. Spaces are allowed. Only the first number is returned:

Example

parseInt("-10");        // returns -10
parseInt("-10.33");     // returns -10
parseInt("10");         // returns 10
parseInt("10.33");      // returns 10
parseInt("10 20 30");   // returns 10
parseInt("10 years");   // returns 10
parseInt("years 10");   // returns NaN

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If the number cannot be converted, NaN (Not a Number) is returned.

The parseFloat() Method

parseFloat() parses a string and returns a number. Spaces are allowed. Only the first number is returned:

Example

parseFloat("10");        // returns 10
parseFloat("10.33");     // returns 10.33
parseFloat("10 20 30");  // returns 10
parseFloat("10 years");  // returns 10
parseFloat("years 10");  // returns NaN

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If the number cannot be converted, NaN (Not a Number) is returned.

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Number Properties

Property	Description
MAX_VALUE	Returns the largest number possible in JavaScript
MIN_VALUE	Returns the smallest number possible in JavaScript
POSITIVE_INFINITY	Represents infinity (returned on overflow)
NEGATIVE_INFINITY	Represents negative infinity (returned on overflow)
NaN	Represents a "Not-a-Number" value

JavaScript MIN_VALUE and MAX_VALUE

MAX_VALUE returns the largest possible number in JavaScript.

Example

var x = Number.MAX_VALUE;

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MIN_VALUE returns the lowest possible number in JavaScript.

Example

var x = Number.MIN_VALUE;

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JavaScript POSITIVE_INFINITY

Example

var x = Number.POSITIVE_INFINITY;

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POSITIVE_INFINITY is returned on overflow:

Example

var x = 1 / 0;

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JavaScript NEGATIVE_INFINITY

Example

var x = Number.NEGATIVE_INFINITY;

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NEGATIVE_INFINITY is returned on overflow:

Example

var x = -1 / 0;

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JavaScript NaN - Not a Number

Example

var x = Number.NaN;

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NaN is a JavaScript reserved word indicating that a number is not a legal number.

Trying to do arithmetic with a non-numeric string will result in NaN (Not a Number):

Example

var x = 100 / "Apple"; // x will be NaN (Not a Number)

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Number Properties Cannot be Used on Variables

Number properties belongs to the JavaScript's number object wrapper called Number.

These properties can only be accessed as Number.MAX_VALUE.

Using myNumber.MAX_VALUE, where myNumber is a variable, expression, or value, will return undefined:

Example

var x = 6;
var y = x.MAX_VALUE; // y becomes undefined

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JavaScript Number Methods