Convert JavaScript parseInt buggy

Question

At startup

console.log(parseInt("9658921879781125")) 

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

Why is this so?

Answer 1

That would be because

 9658921879781125 > Number.MAX_SAFE_INTEGER // true 

Therefore, it is unsafe to try to work with numbers larger than Number.MAX_SAFE_INTEGER

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The constant MAX_SAFE_INTEGER has the value 9007199254740991 (9 007 199 244 740 991 or ~ 9 quadrillion). The rationale for this number is that JavaScript uses double-precision floating-point numbers, as specified in IEEE 754, and can only safely represent numbers between - (2 ⁵³ - 1) and 2 ⁵³ - 1.

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