var a = 2000000000000000000;
a = a - 1; //Doesn't work
a = a + 1; //Doesn't work
But
a = a * 10; //Works
a = a / 10; //Works
Can anyone explain why this happens?
You can try this example in browser console.
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Jeevan
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What do you mean by "doesn't work"? – Oliver Charlesworth May 30 '13 at 10:25
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1Too long int: http://ecma262-5.com/ELS5_HTML.htm#Section_8.5 Other answer on stackoverflow: http://stackoverflow.com/questions/307179/what-is-javascripts-max-int-whats-the-highest-integer-value-a-number-can-go-t#307200 – Ron van der Heijden May 30 '13 at 10:27
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1@OliCharlesworth try it. – Jeevan May 30 '13 at 10:30
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@Jeevan: Not a good response. It would take you two seconds to add the relevant output/error description to your question, thus making it self-contained. – Oliver Charlesworth May 30 '13 at 10:42
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@OliCharlesworth Sorry. Doesn't work means addition is not performed, ie if we do 2 + 1 , We should get 3 as the result. It gives me 2 as the result. – Jeevan May 31 '13 at 11:38
1 Answers
4
You're running into the limits of JavaScript integer calculus.
The largest integer number, JavaScript can use with full precision is 9007199254740992.
Your number is larger and thus will be internally represented as a double. As a consequence you run into all the problems associated with floating point calculus, which you see here.
Sirko
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@Jeevan See, e.g., [Wikipedia on floating point](https://en.wikipedia.org/wiki/Floating_point#Accuracy_problems). – Sirko May 30 '13 at 11:16