Javascript数字实际上是双精度浮点数。可以精确存储的最大整数是2 ⁵³ ，远低于你的2 ⁶³ -1。

Javascript numbers are actually double precision floats. The largest integer that can be precisely stored is 2⁵³, much less then your 2⁶³-1.

alert( Math.pow(2, 53) - 1 ) // 9007199254740991
alert( Math.pow(2, 53)     ) // 9007199254740992
alert( Math.pow(2, 53) + 1 ) // 9007199254740992