number to string conversion error in javascript

Question

Did you ever try to convert a big number to a string in javascript?

Please try this:

var n = 10152557636804775;
console.log(n); // outputs 10152557636804776

Can you help me understand why?

possible duplicate of Why is JavaScript's number *display* for large numbers inaccurate? — Artjom B.
– Artjom B., Commented Oct 24, 2014 at 12:40
possible duplicate of What is JavaScript's highest integer value that a Number can go to without losing precision? — user247702
– user247702, Commented Oct 24, 2014 at 12:40

Community · Accepted Answer · 2017-05-23 12:05:52Z

3

10152557636804775 is higher than the maximum integer number that can be safely represented in JavaScript (it's Number.MAX_SAFE_INTEGER). See also this post for more details.

From MDN (emphasis is mine):

The MAX_SAFE_INTEGER constant has a value of 9007199254740991. 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 -(2^53 - 1) and 2^53 - 1.

To check if a given variable can be safely represented as an integer (without representation errors) you can use IsSafeInteger():

var n = 10152557636804775;
console.assert(Number.isSafeInteger(n) == false);

edited May 23, 2017 at 12:05

CommunityBot

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answered Oct 24, 2014 at 12:39

Adriano Repetti

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