我有一些我不了解的关于javascript Number.MAX_VALUE

Question

为什么会出现＃Number; MAX_VALUE＆＃39;

(Number.MAX_VALUE+123)==Number.MAX_VALUE   //true  why?
(Number.MAX_VALUE+Number.MAX_VALUE)==Number.MAX_VALUE  //false why?
console.log(5.3e-324)  //5e-324 why?