isFinite方法详解

MDN中描述isFinite()函数：确定函数的参数是否为有限数，可以将参数转化为数字，

JS高程设计这样描述isFinite()函数：在参数位于最小与最大数值之间时会返回true

综上：isFinite()方法就是在-Infinity和Infinity之间返回true，否则返回false；

Number.MAX_VALUE + 1 ===  Number.MAX_VALUE + 2   //true
Number.MAX_VALUE + 1 ===  Number.MAX_VALUE + 999999   //true
Number.MAX_VALUE + 1 ===  Number.MAX_VALUE + 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999 // true
运用科学计数法可以这样写：
Number.MAX_VALUE + 1 === Number.MAX_VALUE + （1e+291）

当在增加一个9时，就会变成false
Number.MAX_VALUE + 1 ===  Number.MAX_VALUE + 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999 // false
科学计数法也可以这样写：
Number.MAX_VALUE + 1 === Number.MAX_VALUE + （1e+292）

但是对于乘法却是比较诡异：
Number.MAX_VALUE * 1.00000001 === Infinity

所以：
isFinite(Number.MAX_VALUE * 1.00000001)  //false
isFinite(Number.MAX_VALUE+(Number.MAX_VALUE))   //false

isFinite(Infinity);  // false
isFinite(NaN);       // false
isFinite(-Infinity); // false

isFinite(0);         // true
isFinite(2e64);      // true
isFinite(910);       // true

isFinite(null);      // true

isFinite('0');       // true
isFinite('hello')    //false
isFinite(true)       //true
isFinite(false)      //true

难点就是判断数据是否为正无穷或者负无穷，规则上面已经提到过！

可以参照如下链接：https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isFinite

         https://stackoverflow.com/questions/10837670/adding-to-number-max-value

         https://stackoverflow.com/questions/25532240/isfinitenumber-max-value-1-returns-true