Integers in JavaScript

Question

MDN states:

Numbers in JavaScript are "double-precision 64-bit format IEEE 754 values", according to the spec. This has some interesting consequences. There's no such thing as an integer in JavaScript, so you have to be a little careful with your arithmetic if you're used to math in C or Java.

This suggests all numbers are floats. Is there any way to use integers, not float?

MDN is a great resource and is frequently referenced here at SO. — Andrew Whitaker, Jan 16 '11 at 04:12

score 16 · Accepted Answer · answered Jan 16 '11 at 04:12

There are really only a few data types in Javascript: Objects, numbers, and strings. As you read, JS numbers are all 64-bit floats. There are no ints.

Firefox 4 will have support for Typed Arrays, where you can have arrays of real ints and such: https://developer.mozilla.org/en/JavaScript_typed_arrays

Until then, there are hackish ways to store integer arrays as strings, and plucking out each integers using charCodeAt().

score 4 · Answer 2 · edited Feb 15 '13 at 08:15

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I don't think it ever will support integers. It isn't a problem as every unsigned 32 bit integer can be accurately represented as a 64 bit floating point number.

Modern JavaScript engines could be smart enough to generate special code when the numbers are integer (with safeguard checks to make sure of it), but I'm not sure.

edited Feb 15 '13 at 08:15

Thanatos

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answered Jan 16 '11 at 04:10

Axel Gneiting

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All JS engines (SpiderMonkey's has from its very first implementation — the first JS engine) have used int32-maths when possible. – gsnedders Jan 16 '11 at 14:27
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It isn't a problem... until you want a 64-bit int or larger. – Thanatos Feb 15 '13 at 08:14
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well, it can be a quite big problem actually. If you send 100000 integers to javascript and asks it to summarize, the floating point problems might give you quite strange answers. That is why I found this question. – Nicklas Avén Jun 02 '13 at 21:30

qwertymk · Answer 3 · 2011-01-16T04:48:20.050

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Use this:

function int(a) { return Math.floor(a); }

And yo can use it like this:

var result = int(2.1 + 8.7 + 9.3); //int(20.1)
alert(result);                     //alerts 20

edited Jan 16 '11 at 04:48

answered Jan 16 '11 at 04:23

qwertymk

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Is there any point at all in this other than creating a slightly alias of `Math.floor`? – Yi Jiang Jan 16 '11 at 04:59
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I would use `var int = Math.floor;` to avoid the extra function call. – ChaosPandion Jan 16 '11 at 06:23
Is there any reason not to just do `(a | 0)`? – Mike Samuel Jan 16 '11 at 22:13
@MikeSamuel, binary bitwise operations convert operands to 32bit integers, so bits 32-51 would be lost. – weaknespase Sep 29 '15 at 16:29
@Valentin, Loss of precision is important, but the question asked about "C++ `int`s" which only have 32b on many widely-used architectures so it's not clear that there is a loss of precision from the askers point of view. – Mike Samuel Sep 29 '15 at 16:42

score 0 · Answer 4 · answered Jan 16 '11 at 04:14

0

There is zero support for integers. It should be a simple matter of rounding off a variable every time you need it. The performance overhead isn't bad at all.

answered Jan 16 '11 at 04:14

score 0 · Answer 5 · answered Jan 16 '11 at 04:17

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If you really need to use integers, just use the floor method on each number you encounter.

Other than that, the loose typing of Javascript is one of it's strengths.

answered Jan 16 '11 at 04:17

ryebr3ad

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Integers in JavaScript

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