Convert GUID (UUID) to integer numbers in Javascript (and back again)

explanation.js

// A UUID is a 128-bit number which is too large to be represented as a native integer in Javascript.
// The original solution I posted (based on https://github.com/uuidjs/uuid#uuidparsestr ) wasn't good,
// as it converted the given UUID into a byte array and then selected only the first four bytes to be
// used as the integer.

const uuid = require('uuid');

let convertGuidToInt = (uuid) => {
    // parse accountId into Uint8Array[16] variable
    let parsedUuid = uuid.parse(uuid);
    console.log(`uuid ${uuid} parsed successfully`);

    // convert to integer - see answers to https://stackoverflow.com/q/39346517/2860309
    let buffer = Buffer.from(parsedUuid);
    console.log(`parsed uuid converted to buffer`);
    let result = buffer.readUInt32BE(0);
    console.log(`buffer converted to integer ${result} successfully`);

    return result;
},

// The above example drops most of the number and so is a) impossible to convert back to UUID
// and b) unlikely to ensure uniqueness. In response to the requests for a way to convert the
// resulting integers back to UUIDs, here is the code to convert UUIDs to BigNumber objects
// and back again using the bignumber.js package:

const BigNumber = require('bignumber.js');

let convertGuidToInt = (id) => {
    // remove the dashes from the given uuid and convert to a hexadecimal BigNumber object
    const bn = new BigNumber(id.replace(/-/g, ''), 16);
    // return the string representation of the BigNumber object as a decimal
    return bn.toString(10);
};

let convertIntToGuid = (num) => {
    // convert the string representation of the decimal number to a BigNumber object
    const bn = new BigNumber(num, 10);
    // convert the BigNumber to a hexadecimal string
    const id = bn.toString(16);
    // return the string with the dashes (8-4-4-4-12)
    return `${id.substr(0, 8)}-${id.substr(8, 4)}-${id.substr(12, 4)}-${id.substr(16, 4)}-${id.substr(20)}`;
};

uuidToInt.js

const BigNumber = require('bignumber.js');

let convertGuidToInt = (id) => {
    // remove the dashes from the given uuid and convert to a hexadecimal BigNumber object
    const bn = new BigNumber(id.replace(/-/g, ''), 16);
    // return the decimal representation of the BigNumber object as a string
    return bn.toString(10);
};

let convertIntToGuid = (num) => {
    // convert the string representation of the decimal number to a BigNumber object
    const bn = new BigNumber(num, 10);
    // convert the BigNumber to a hexadecimal string
    const id = bn.toString(16);
    // return the string with the dashes (8-4-4-4-12)
    return `${id.substr(0, 8)}-${id.substr(8, 4)}-${id.substr(12, 4)}-${id.substr(16, 4)}-${id.substr(20)}`;
};

@Pitshopdirect @mikepiven @DamithaPerera I I've just updated the gist with an explanation for why the original method isn't reversible and added an improved method.

Please note that the improved method only works if the integer value can continue to be represented as a string (or a BigNumber object) because Javascript's numbers aren't large enough to support UUIDs.

Your mileage may vary.