JavaScript uses IEEE 754 double-precision floats to represents numbers. That works perfectly fine for small numbers, however, it is an issue for big integers. This means they lose integer precision for values beyond +/- 2 pow 53

Problem

Presentation of small integer in decimal format works fine (e.g. 0x1FF). However, we can see an issue when try to convert big integers like 0x1234567890abcdeffedcba908765421 to string decimal.

(0x1FF).toString(10) // returns '511' - correct
(0x1234567890abcdeffedcba908765421).toString(10) // returns '1.5123660750094533e+36' - incorrect - lose integer precision

Solution

Node.js biguint-format module has been built in order to help display very large unsigned integers without any integer precision lose. biguint-format takes an array of bytes (values from 0 to 255) or node Buffer and converts it to decimal format.

var biguint  = require('biguint-format');
 
// 0x1234567890abcdeffedcba908765421 split into bytes
biguint.toDecimalString([0x1, 0x23, 0x45, 0x67, 0x89, 0x0a, 0xbc, 0xde, 0xff, 0xed, 0xcb, 0xa9, 0x08, 0x76, 0x54, 0x21])
 
// output value is '1512366075009453296626403467035300897' - no integer precision lose

biguint-format can also take array of bytes in Big Endian (BE - default value) and Little Endian (LE) formats. Check wikipedia for more details.

var biguint  = require('biguint-format');
 
var buffer1 = new Buffer([0x63, 0xA7, 0x27]);
var buffer2 = new Buffer([0x27, 0xA7, 0x63]);
 
biguint.toDecimalString(buffer1, 'LE') // returns '2598755'
biguint.toDecimalString(buffer2, 'BE') // returns '2598755'
biguint.toDecimalString(buffer2)       // returns '2598755'