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。
javascript只有一个单一的数字类型了，他在内部被表示为64位的浮点数，和java的double一样。
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。
The value NaN is a number value that is the result of an operation that cannot producea normal result. NaN is not equal to any value, including itself. You can detect NaN with the isNaN(number) function.
NaN是一个数值，表示一个不能产生正常结果的运算结果，NaN不等于任何值，包括它自己。可以用isNaN来检查
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.