Very strange error in console.log of Javascript Array

Question

I posted a related question here: Error when removing duplicates from Javascript Array but there's a part of it that might need its own question, so I'll ask it here.

I have this code:

var myArray = [621608617992776, 10156938936550295];
console.log(myArray);

It's a simple array with two numbers. However, when I run the code with the console open. It's increasing the second number by 1.

So instead of console.logging [621608617992776, 10156938936550295]

It's console.logging [621608617992776, 10156938936550296]

Does anyone know why it's doing this?