JavaScript Number Methods
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):
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);
Try
it Yourself »
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:
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);
Try it Yourself »
The valueOf() Method
valueOf() returns a number as a number.
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");
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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.
The Number() method returns the number of milliseconds since 1.1.1970.
The number of milliseconds between 1970-01-02 and 1970-01-01 is 86400000:
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");
Try
it Yourself »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");
Try
it Yourself »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.
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.
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");
Try
it Yourself »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");
Try
it Yourself »If the number cannot be converted, NaN (Not a Number) is returned.
Complete JavaScript Number Reference
For a complete Number reference, visit our:
Complete JavaScript Number Reference.
The reference contains descriptions and examples of all Number properties and methods.
