1  JavaScript Numbers are represented as [IEEE 754 double-precision floats](http://steve.hollasch.net/cgindex/coding/ieeefloat.html).  Unfortunately, this means they lose integer precision for values beyond +/- 2^^53.  For projects that need to accurately handle 64-bit ints, such as [node-thrift](https://github.com/wadey/node-thrift), a performant, Number-like class is needed.  Int64 is that class.
 2  
 3  Int64 instances look and feel much like JS-native Numbers.  By way of example ...
 4  ```js
 5  // First, let's illustrate the problem ...
 6  > (0x123456789).toString(16)
 7  '123456789' // <- what we expect.
 8  > (0x123456789abcdef0).toString(16)
 9  '123456789abcdf00' // <- Ugh!  JS doesn't do big ints. :(
10  
11  // So let's create a couple Int64s using the above values ...
12  
13  // Require, of course
14  > Int64 = require('node-int64')
15  
16  // x's value is what we expect (the decimal value of 0x123456789)
17  > x = new Int64(0x123456789)
18  [Int64 value:4886718345 octets:00 00 00 01 23 45 67 89]
19  
20  // y's value is Infinity because it's outside the range of integer
21  // precision.  But that's okay - it's still useful because it's internal
22  // representation (octets) is what we passed in
23  > y = new Int64('123456789abcdef0')
24  [Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
25  
26  // Let's do some math.  Int64's behave like Numbers.  (Sorry, Int64 isn't
27  // for doing 64-bit integer arithmetic (yet) - it's just for carrying
28  // around int64 values
29  > x + 1
30  4886718346
31  > y + 1
32  Infinity
33  
34  // Int64 string operations ...
35  > 'value: ' + x
36  'value: 4886718345'
37  > 'value: ' + y
38  'value: Infinity'
39  > x.toString(2)
40  '100100011010001010110011110001001'
41  > y.toString(2)
42  'Infinity'
43  
44  // Use JS's isFinite() method to see if the Int64 value is in the
45  // integer-precise range of JS values
46  > isFinite(x)
47  true
48  > isFinite(y)
49  false
50  
51  // Get an octet string representation.  (Yay, y is what we put in!)
52  > x.toOctetString()
53  '0000000123456789'
54  > y.toOctetString()
55  '123456789abcdef0'
56  
57  // Finally, some other ways to create Int64s ...
58  
59  // Pass hi/lo words
60  > new Int64(0x12345678, 0x9abcdef0)
61  [Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
62  
63  // Pass a Buffer
64  > new Int64(new Buffer([0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0]))
65  [Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
66  
67  // Pass a Buffer and offset
68  > new Int64(new Buffer([0,0,0,0,0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0]), 4)
69  [Int64 value:Infinity octets:12 34 56 78 9a bc de f0]
70  
71  // Pull out into a buffer
72  > new Int64(new Buffer([0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0])).toBuffer()
73  <Buffer 12 34 56 78 9a bc de f0>
74  
75  // Or copy into an existing one (at an offset)
76  > var buf = new Buffer(1024);
77  > new Int64(new Buffer([0x12, 0x34, 0x56, 0x78, 0x9a, 0xbc, 0xde, 0xf0])).copy(buf, 512);
78  ```