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");
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 Object Methods

These object methods belong to the Number object:

Method	Description
Number.isInteger()	Returns true if the argument is an integer
Number.isSafeInteger()	Returns true if the argument is a safe integer
Number.parseFloat()	Converts a string to a number
Number.parseInt()	Converts a string to a whole number

Number Methods Cannot be Used on Variables

The number methods above belong to the JavaScript Number Object.

These methods can only be accessed like Number.isInteger().

Using X.isInteger() where X is a variable, will result in an error:

TypeError X.isInteger is not a function.

The Number.isInteger() Method

The Number.isInteger() method returns true if the argument is an integer.

Example

Number.isInteger(10);
Number.isInteger(10.5);

The Number.isSafeInteger() Method

A safe integer is an integer that can be exactly represented as a double precision number.

The Number.isSafeInteger() method returns true if the argument is a safe integer.

Example

Number.isSafeInteger(10);
Number.isSafeInteger(12345678901234567890);

Safe integers are all integers from -(2⁵³ - 1) to +(2⁵³ - 1).
This is safe: 9007199254740991. This is not safe: 9007199254740992.

The Number.parseFloat() Method

Number.parseFloat() parses a string and returns a number.

Spaces are allowed. Only the first number is returned:

Example

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

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

Note

The Number methods Number.parseInt() and Number.parseFloat()

are the same as the

Global methods parseInt() and parseFloat().

The purpose is modularization of globals (to make it easier to use the same JavaScript code outside the browser).

The Number.parseInt() Method

Number.parseInt() parses a string and returns a whole number.

Spaces are allowed. Only the first number is returned:

Example

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

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

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JavaScript Number Methods