JavaScript Number Methods

These number methods can be used on all JavaScript numbers:

Method	Description
toString()	Returns a number as a string
toExponential()	Returns a number written in exponential notation
toFixed()	Returns a number written with a number of decimals
toPrecision()	Returns a number written with a specified length
valueOf()	Returns a number as a number

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

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:

Example

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:

Example

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

toFixed(2) is perfect for working with money.

The toPrecision() Method

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

Example

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.

Example

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.

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

Converting Variables to Numbers

There are 3 JavaScript methods that can be used to convert a variable to a number:

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 a whole number

The methods above are not number methods. They are global JavaScript methods.

The Number() Method

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

Example

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

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("1970-01-01"))

Note

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

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

Example

Number(new Date("1970-01-02"))

Example

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:

Example

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:

Example

parseFloat("10"