JS 基础1： 理解number 数据类型 和隐式类型转换

Posted 2020-08-09

1， javascript only has one type of numberic data, named "number". You can see this reflected in the behavior of the typeof operator, which classifies intergers and floating-point numbers alike simply as numbers:

typeof 10;   // "number"
typeof 10.3;  // "number"
typeof -1.5;  // "number"

2,  In fact, all numbers are double-precision floating-point numbers, known as "doubles", which is 64-bit encolding of numbers, keep in mind that doubles can represent intergers perfectly with up to 53 bits of precison. All of the integers  from -2⁵³ to 2⁵³ are valid doubles. 

3, Note that floating-point numbers are inaccurate when in arithmetic, for example, 0.1+0.2 => 0.30000000000004;

It is better to tranform the floating-point  number to intergers for calculation. 10 + 20 => 30;

-----------------------------------------------------------------------------------------------------------------------------------

4， coercisons can also hide errors(隐式类型转换可能隐藏错误)。

　　an undefined variable will convert to the NaN in an arithmetic calculation,  which causes the calculation ot continue with often confusing and unprdictable results.