JavaScript Number Methods

Number methods help you work with numbers.

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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.

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The toString() Method

toString() 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+0x.toExponential(4);     // returns 9.6560e+0x.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.

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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 10x.toFixed(2);           // returns 9.66x.toFixed(4);           // returns 9.6560x.toFixed(6);           // returns 9.656000

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toFixed(2) is perfect for working with money.

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The toPrecision() Method

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

Example

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

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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.

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Global 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

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The Number() Method

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

Example

x = true;
Number(x);        // returns 1x = false;     
Number(x);        // returns 0x = new Date();
Number(x);        // returns 1404568027739x = "10"
Number(x);        // returns 10x = "10 20"
Number(x);        // returns NaN

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Used on Date(), the Number() method returns the number of milliseconds since 1.1.1970.

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

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

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The parseFloat() Method

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

Example

parseFloat("10");        // returns 10parseFloat("10.33");     // returns 10.33parseFloat("10 20 30");  // returns 10parseFloat("10 years");  // returns 10parseFloat("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
NEGATIVE_INFINITY	Represents negative infinity (returned on overflow)
NaN	Represents a "Not-a-Number" value
POSITIVE_INFINITY	Represents infinity (returned on overflow)

Example

var x = Number.MAX_VALUE;

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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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