Speaking JavaScript

Chapter 11. Numbers

JavaScript has a single type for all numbers: it treats all of them as floating-point numbers. However, the dot is not displayed if there are no digits after the decimal point:

> 5.000
5

Internally, most JavaScript engines optimize and do distinguish between floating-point numbers and integers (details: Integers in JavaScript). But that is something that programmers don’t see.

JavaScript numbers are double (64-bit) values, based on the IEEE Standard for Floating-Point Arithmetic (IEEE 754). That standard is used by many programming languages.

Number Literals

A number literal can be an integer, floating point, or (integer) hexadecimal:

> 35  // integer
35
> 3.141  // floating point
3.141
> 0xFF  // hexadecimal
255

Exponent

An exponent, eX, is an abbreviation for “multiply with 10^X”:

> 5e2
500
> 5e-2
0.05
> 0.5e2
50

Invoking Methods on Literals

With number literals, the dot for accessing a property must be distinguished from the decimal dot. This leaves you with the following options if you want to invoke toString() on the number literal 123:

123..toString()
123 .toString()  // space before the dot
123.0.toString()
(123).toString()

Converting to Number

Values are converted to numbers as follows:

Value	Result
undefined	NaN
null	0
A boolean	false → 0
true → 1
A number	Same as input (nothing to convert)
A string	Parse the number in the string (ignoring leading and trailing whitespace); the empty string is converted to 0. Example: '3.141' → 3.141
An object	Call ToPrimitive(value, Number) (see ...