JavaScript Number Methods

Number methods help you work with numbers.

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):

let x = 123;
x.toString();
(123).toString();
(100 + 23).toString();

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:

let x = 9.656;
x.toExponential(2);
x.toExponential(4);
x.toExponential(6);

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:

let x = 9.656;
x.toFixed(0);
x.toFixed(2);
x.toFixed(4);
x.toFixed(6);

The toPrecision() Method

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

let x = 9.656;
x.toPrecision();
x.toPrecision(2);
x.toPrecision(4);
x.toPrecision(6);

The valueOf() Method

valueOf() returns a number as a number.

let x = 123;
x.valueOf();
(123).valueOf();
(100 + 23).valueOf();

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.

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:

The Number() Method

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

Number(true);
Number(false);
Number("10");
Number("  10");
Number("10  ");
Number(" 10  ");
Number("10.33");
Number("10,33");
Number("10 33");
Number("John");

The Number() Method Used on Dates

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

Number(new Date("1970-01-01"))

The number of milliseconds between 1970-01-02 and 1970-01-01 is 86400000:

Number(new Date("1970-01-02"))

Number(new Date("2017-09-30"))

The parseInt() Method

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

parseInt("-10");
parseInt("-10.33");
parseInt("10");
parseInt("10.33");
parseInt("10 20 30");
parseInt("10 years");
parseInt("years 10");

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:

parseFloat("10");
parseFloat("10.33");
parseFloat("10 20 30");
parseFloat("10 years");
parseFloat("years 10");

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

Number Properties

JavaScript MIN_VALUE and MAX_VALUE

MAX_VALUE returns the largest possible number in JavaScript.

let x = Number.MAX_VALUE;

MIN_VALUE returns the lowest possible number in JavaScript.

let x = Number.MIN_VALUE;

JavaScript POSITIVE_INFINITY

let x = Number.POSITIVE_INFINITY;

POSITIVE_INFINITY is returned on overflow:

let x = 1 / 0;

JavaScript NEGATIVE_INFINITY

let x = Number.NEGATIVE_INFINITY;

NEGATIVE_INFINITY is returned on overflow:

let x = -1 / 0;

JavaScript NaN – Not a Number

let x = Number.NaN;

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):

let x = 100 / "Apple";

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:

let x = 6;
x.MAX_VALUE

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