Javascript function is mutating parameter with node v14.7.0

Question

Node.js is mutating the number value passed into the test function. Any idea why and how to fix? Thank you!

const val1  = 61368443939717130;
const val2 = 861368443939717130;
const val3 = 161368443939717130;

const test = (v) => {
  console.log(v);
}

test(val1);
test(val2);
test(val3);

// Output:
// 61368443939717130
// 861368443939717100
// 161368443939717120

Nothing is being mutated here. You're just hitting the limits of how big a number in JS can be. Look up `bigInt` — Dominik, Aug 07 '21 at 23:33
Does this answer your question? [What is JavaScript's highest integer value that a number can go to without losing precision?](https://stackoverflow.com/questions/307179/what-is-javascripts-highest-integer-value-that-a-number-can-go-to-without-losin) — tevemadar, Aug 07 '21 at 23:37

score 0 · Answer 1 · answered Aug 07 '21 at 23:39

It's because the number 161368443939717130 is bigger than the maximum safe integer that Javascript can represent, which is provided by the constant Number.MAX_SAFE_INTEGER. When working with big numbers you should always check that the values are below the limit, or otherwise you will get unexpected results. See more info here.

score 0 · Answer 2 · answered Aug 08 '21 at 00:47

Your numbers are out of range for javascript.

The max number javascript can handle is 9007199254740991 (9,007,199,254,740,991 or ~9 quadrillion).

It is represented by the MAX_SAFE_INTEGER variable. 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 integers between -(2^53 - 1) and 2^53 - 1.

Use BigInt, which has no practical upper limit. But BigInt can’t handle decimals. This means that if you convert from a Number to a BigInt and backward again, you can lose precision.

console.log(Number.MAX_SAFE_INTEGER)
// 9007199254740991
console.log(Number.MAX_SAFE_INTEGER + 10)
// 9007199254741000
console.log(BigInt(Number.MAX_SAFE_INTEGER) + 10n) 
// 9007199254741001n

Javascript function is mutating parameter with node v14.7.0

2 Answers2