JavaScript parseInt conversion is buggy [duplicate]

Question

When running

   console.log(parseInt("9658921879781125"))

it gives a value of 9658921879781124, which is less than the original value.

Why is this the case?

Answer 1

That would be because

9658921879781125 > Number.MAX_SAFE_INTEGER // true

So it is unsafe to try to work with numbers greater than Number.MAX_SAFE_INTEGER

---

The MAX_SAFE_INTEGER constant has a value of 9007199254740991 (9,007,199,254,740,991 or ~9 quadrillion). The reasoning behind that number is that JavaScript uses double-precision floating-point format numbers as specified in IEEE 754 and can only safely represent numbers between -(2⁵³ - 1) and 2⁵³ - 1.

Safe in this context refers to the ability to represent integers exactly and to correctly compare them.