JavaScript has a single number type. Internally, it is represented as 64-bit floating point, the same as Java's double. Unlike most other programming languages, there is no separate integer type, so 1 and 1.0 are the same value. This is a significant convenience because problems of overflow in short integers are completely avoided, and all you need to know about a number is that it is a number. A large class of numeric type errors is avoided.

If a number literal has an exponent part, then the value of the literal is computed by multiplying the part before the e by 10 raised to the power of the part after the e. So 100 and 1e2 are the same number.

Negative numbers can be formed by using the - prefix operator.

The value NaN is a number value that is the result of an operation that cannot produce a normal result. NaN is not equal to any value, including itself. You can detect NaN with the isNaN( number ) function.

The value Infinity represents all values greater than 1.79769313486231570e+308.

Numbers have methods (see Chapter 8). JavaScript has a Math object that contains a set of methods that act on numbers. For example, the Math.floor( number ) method can be used to convert a number into an integer.