Why the number 9094504735860991 is translated to 9094504735860992 in javascript?

Asked Apr 11 '17 at 14:49

Active Apr 11 '17 at 14:51

Viewed 43 times

var num = 9094504735860991;
console.log(num); // 9094504735860992

Now I set a variable named num equals to 9094504735860991,but when logged, it changed to 9094504735860992.

Number.MAX_VALUE => 2^53 - 1 === 9007199254740000, however 9094504735860991 < 9007199254740000.

edited Apr 11 '17 at 14:51

asked Apr 11 '17 at 14:49

王吉志

1

you mean **9094504735860991 > 9007199254740000** right? – Matteo Tassinari Apr 11 '17 at 14:50
1

We'd need to see some code for more context into why this is happening. – Stese Apr 11 '17 at 14:51
Are you sure that's Number.MAX_VALUE? – Oliver Charlesworth Apr 11 '17 at 14:52
2

Short answer: Because beyond `Number.MAX_SAFE_INTEGER + 1` (`9007199254740991`), the IEEE-754 floating-point format can no longer represent every consecutive integer. `9007199254740991 + 1` is `9007199254740992`, but `9007199254740992 + 1` is also ``9007199254740992` because `9007199254740993` cannot be represented. The next that can be is `9007199254740994`. Long answer: See the linked question's answers. – T.J. Crowder Apr 11 '17 at 14:56
@T.J.Crowder - Please post this as an answer. Would help others!! – Pugazh Apr 11 '17 at 14:59
@Pugazh: Thanks. :-) Maybe I'll update [my answer to the linked question](http://stackoverflow.com/a/1379973/157247), which looks like it could be clearer via incorporating some of my comment above. – T.J. Crowder Apr 11 '17 at 15:04
Ugh, I wish I could fix the error in my comment above. `Number.MAX_SAFE_INTEGER + 1` is `9007199254740992`, not `9007199254740991`, `900719925474099` **is** `Number.MAX_SAFE_INTEGER`. – T.J. Crowder Apr 11 '17 at 15:48

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