web3.utils

This package provides utility functions for Ethereum dapps and other web3.js packages.

Bloom Filters

What are bloom filters?

A Bloom filter is a probabilistic, space-efficient data structure used for fast checks of set membership. That probably doesn’t mean much to you yet, and so let’s explore how bloom filters might be used.

Imagine that we have some large set of data, and we want to be able to quickly test if some element is currently in that set. The naive way of checking might be to query the set to see if our element is in there. That’s probably fine if our data set is relatively small. Unfortunately, if our data set is really big, this search might take a while. Luckily, we have tricks to speed things up in the ethereum world!

A bloom filter is one of these tricks. The basic idea behind the Bloom filter is to hash each new element that goes into the data set, take certain bits from this hash, and then use those bits to fill in parts of a fixed-size bit array (e.g. set certain bits to 1). This bit array is called a bloom filter.

Later, when we want to check if an element is in the set, we simply hash the element and check that the right bits are in the bloom filter. If at least one of the bits is 0, then the element definitely isn’t in our data set! If all of the bits are 1, then the element might be in the data set, but we need to actually query the database to be sure. So we might have false positives, but we’ll never have false negatives. This can greatly reduce the number of database queries we have to make.

Real Life Example

An ethereum real life example in where this is useful is if you want to update a users balance on every new block so it stays as close to real time as possible. Without using a bloom filter on every new block you would have to force the balances even if that user may not of had any activity within that block. But if you use the logBlooms from the block you can test the bloom filter against the users ethereum address before you do any more slow operations, this will dramatically decrease the amount of calls you do as you will only be doing those extra operations if that ethereum address is within that block (minus the false positives outcome which will be negligible). This will be highly performant for your app.

randomHex

web3.utils.randomHex(size)

The randomHex library to generate cryptographically strong pseudo-random HEX strings from a given byte size.

Parameters

  1. size - Number: The byte size for the HEX string, e.g. 32 will result in a 32 bytes HEX string with 64 characters prefixed with “0x”.

Returns

String: The generated random HEX string.

Example

web3.utils.randomHex(32)
> "0xa5b9d60f32436310afebcfda832817a68921beb782fabf7915cc0460b443116a"

web3.utils.randomHex(4)
> "0x6892ffc6"

web3.utils.randomHex(2)
> "0x99d6"

web3.utils.randomHex(1)
> "0x9a"

web3.utils.randomHex(0)
> "0x"

BN

web3.utils.BN(mixed)

The BN.js library for calculating with big numbers in JavaScript. See the BN.js documentation for details.

Note

For safe conversion of many types, incl BigNumber.js use utils.toBN

Parameters

  1. mixed - String|Number: A number, number string or HEX string to convert to a BN object.

Returns

Object: The BN.js instance.

Example

var BN = web3.utils.BN;

new BN(1234).toString();
> "1234"

new BN('1234').add(new BN('1')).toString();
> "1235"

new BN('0xea').toString();
> "234"

isBN

web3.utils.isBN(bn)

Checks if a given value is a BN.js instance.

Parameters

  1. bn - Object: A BN.js instance.

Returns

Boolean

Example

var number = new BN(10);

web3.utils.isBN(number);
> true

isBigNumber

web3.utils.isBigNumber(bignumber)

Checks if a given value is a BigNumber.js instance.

Parameters

  1. bignumber - Object: A BigNumber.js instance.

Returns

Boolean

Example

var number = new BigNumber(10);

web3.utils.isBigNumber(number);
> true

sha3

web3.utils.sha3(string)
web3.utils.keccak256(string) // ALIAS

Will calculate the sha3 of the input.

Note

To mimic the sha3 behaviour of solidity use soliditySha3

Parameters

  1. string - String: A string to hash.

Returns

String: the result hash.

Example

web3.utils.sha3('234'); // taken as string
> "0xc1912fee45d61c87cc5ea59dae311904cd86b84fee17cc96966216f811ce6a79"

web3.utils.sha3(new BN('234'));
> "0xbc36789e7a1e281436464229828f817d6612f7b477d66591ff96a9e064bcc98a"

web3.utils.sha3(234);
> null // can't calculate the hash of a number

web3.utils.sha3(0xea); // same as above, just the HEX representation of the number
> null

web3.utils.sha3('0xea'); // will be converted to a byte array first, and then hashed
> "0x2f20677459120677484f7104c76deb6846a2c071f9b3152c103bb12cd54d1a4a"

sha3Raw

web3.utils.sha3Raw(string)

Will calculate the sha3 of the input but does return the hash value instead of null if for example an empty string is passed.

Note

Further details about this function can be seen here sha3

soliditySha3

web3.utils.soliditySha3(param1 [, param2, ...])

Will calculate the sha3 of given input parameters in the same way solidity would. This means arguments will be ABI converted and tightly packed before being hashed.

Warning

This method poses a security risk where multiple inputs can compute to the same hash. Provided in the example code are multiple cases of this security risk

Parameters

  1. paramX - Mixed: Any type, or an object with {type: 'uint', value: '123456'} or {t: 'bytes', v: '0xfff456'}. Basic types are autodetected as follows:

    • String non numerical UTF-8 string is interpreted as string.
    • String|Number|BN|HEX positive number is interpreted as uint256.
    • String|Number|BN negative number is interpreted as int256.
    • Boolean as bool.
    • String HEX string with leading 0x is interpreted as bytes.
    • HEX HEX number representation is interpreted as uint256.

Returns

String: the result hash.

Example

// As a short example of the non-distinguished nature of
// Solidity tight-packing (which is why it is inappropriate
// for many things from a security point of view), consider
// the following examples are all equal, despite representing
// very different values and layouts.
web3.utils.soliditySha3('hello','world01')
// "0xfb0a9d38c4dc568cbd105866540986fabf3c08c1bfb78299ce21aa0e5c0c586b"
web3.utils.soliditySha3({type: 'string', value: 'helloworld'},{type: 'string', value: '01'})
// "0xfb0a9d38c4dc568cbd105866540986fabf3c08c1bfb78299ce21aa0e5c0c586b"
web3.utils.soliditySha3({type: 'string', value: 'hell'},{type: 'string', value: 'oworld'},{type: 'uint16', value: 0x3031})
// "0xfb0a9d38c4dc568cbd105866540986fabf3c08c1bfb78299ce21aa0e5c0c586b"
web3.utils.soliditySha3({type: 'uint96', value: '32309054545061485574011236401'})
// "0xfb0a9d38c4dc568cbd105866540986fabf3c08c1bfb78299ce21aa0e5c0c586b"

web3.utils.soliditySha3('234564535', '0xfff23243', true, -10);
// auto detects:        uint256,      bytes,     bool,   int256
> "0x3e27a893dc40ef8a7f0841d96639de2f58a132be5ae466d40087a2cfa83b7179"


web3.utils.soliditySha3('Hello!%'); // auto detects: string
> "0x661136a4267dba9ccdf6bfddb7c00e714de936674c4bdb065a531cf1cb15c7fc"


web3.utils.soliditySha3('234'); // auto detects: uint256
> "0x61c831beab28d67d1bb40b5ae1a11e2757fa842f031a2d0bc94a7867bc5d26c2"

web3.utils.soliditySha3(0xea); // same as above
> "0x61c831beab28d67d1bb40b5ae1a11e2757fa842f031a2d0bc94a7867bc5d26c2"

web3.utils.soliditySha3(new BN('234')); // same as above
> "0x61c831beab28d67d1bb40b5ae1a11e2757fa842f031a2d0bc94a7867bc5d26c2"

web3.utils.soliditySha3({type: 'uint256', value: '234'})); // same as above
> "0x61c831beab28d67d1bb40b5ae1a11e2757fa842f031a2d0bc94a7867bc5d26c2"

web3.utils.soliditySha3({t: 'uint', v: new BN('234')})); // same as above
> "0x61c831beab28d67d1bb40b5ae1a11e2757fa842f031a2d0bc94a7867bc5d26c2"


web3.utils.soliditySha3('0x407D73d8a49eeb85D32Cf465507dd71d507100c1');
> "0x4e8ebbefa452077428f93c9520d3edd60594ff452a29ac7d2ccc11d47f3ab95b"

web3.utils.soliditySha3({t: 'bytes', v: '0x407D73d8a49eeb85D32Cf465507dd71d507100c1'});
> "0x4e8ebbefa452077428f93c9520d3edd60594ff452a29ac7d2ccc11d47f3ab95b" // same result as above


web3.utils.soliditySha3({t: 'address', v: '0x407D73d8a49eeb85D32Cf465507dd71d507100c1'});
> "0x4e8ebbefa452077428f93c9520d3edd60594ff452a29ac7d2ccc11d47f3ab95b" // same as above, but will do a checksum check, if its multi case


web3.utils.soliditySha3({t: 'bytes32', v: '0x407D73d8a49eeb85D32Cf465507dd71d507100c1'});
> "0x3c69a194aaf415ba5d6afca734660d0a3d45acdc05d54cd1ca89a8988e7625b4" // different result as above


web3.utils.soliditySha3({t: 'string', v: 'Hello!%'}, {t: 'int8', v:-23}, {t: 'address', v: '0x85F43D8a49eeB85d32Cf465507DD71d507100C1d'});
> "0xa13b31627c1ed7aaded5aecec71baf02fe123797fffd45e662eac8e06fbe4955"

soliditySha3Raw

web3.utils.soliditySha3Raw(param1 [, param2, ...])

Will calculate the sha3 of given input parameters in the same way solidity would. This means arguments will be ABI converted and tightly packed before being hashed. The difference between this function and the soliditySha3 function is that it will return the hash value instead of null if for example an empty string is given.

Note

Further details about this function can be seen here soliditySha3

isHex

web3.utils.isHex(hex)

Checks if a given string is a HEX string.

Parameters

  1. hex - String|HEX: The given HEX string.

Returns

Boolean

Example

web3.utils.isHex('0xc1912');
> true

web3.utils.isHex(0xc1912);
> true

web3.utils.isHex('c1912');
> true

web3.utils.isHex(345);
> true // this is tricky, as 345 can be a a HEX representation or a number, be careful when not having a 0x in front!

web3.utils.isHex('0xZ1912');
> false

web3.utils.isHex('Hello');
> false

isHexStrict

web3.utils.isHexStrict(hex)

Checks if a given string is a HEX string. Difference to web3.utils.isHex() is that it expects HEX to be prefixed with 0x.

Parameters

  1. hex - String|HEX: The given HEX string.

Returns

Boolean

Example

web3.utils.isHexStrict('0xc1912');
> true

web3.utils.isHexStrict(0xc1912);
> false

web3.utils.isHexStrict('c1912');
> false

web3.utils.isHexStrict(345);
> false // this is tricky, as 345 can be a a HEX representation or a number, be careful when not having a 0x in front!

web3.utils.isHexStrict('0xZ1912');
> false

web3.utils.isHex('Hello');
> false

isAddress

web3.utils.isAddress(address)

Checks if a given string is a valid Ethereum address. It will also check the checksum, if the address has upper and lowercase letters.

Parameters

  1. address - String: An address string.

Returns

Boolean

Example

web3.utils.isAddress('0xc1912fee45d61c87cc5ea59dae31190fffff232d');
> true

web3.utils.isAddress('c1912fee45d61c87cc5ea59dae31190fffff232d');
> true

web3.utils.isAddress('0XC1912FEE45D61C87CC5EA59DAE31190FFFFF232D');
> true // as all is uppercase, no checksum will be checked

web3.utils.isAddress('0xc1912fEE45d61C87Cc5EA59DaE31190FFFFf232d');
> true

web3.utils.isAddress('0xC1912fEE45d61C87Cc5EA59DaE31190FFFFf232d');
> false // wrong checksum

toChecksumAddress

web3.utils.toChecksumAddress(address)

Will convert an upper or lowercase Ethereum address to a checksum address.

Parameters

  1. address - String: An address string.

Returns

String: The checksum address.

Example

web3.utils.toChecksumAddress('0xc1912fee45d61c87cc5ea59dae31190fffff232d');
> "0xc1912fEE45d61C87Cc5EA59DaE31190FFFFf232d"

web3.utils.toChecksumAddress('0XC1912FEE45D61C87CC5EA59DAE31190FFFFF232D');
> "0xc1912fEE45d61C87Cc5EA59DaE31190FFFFf232d" // same as above

checkAddressChecksum

web3.utils.checkAddressChecksum(address)

Checks the checksum of a given address. Will also return false on non-checksum addresses.

Parameters

  1. address - String: An address string.

Returns

Boolean: true when the checksum of the address is valid, false if it’s not a checksum address, or the checksum is invalid.

Example

web3.utils.checkAddressChecksum('0xc1912fEE45d61C87Cc5EA59DaE31190FFFFf232d');
> true

toHex

web3.utils.toHex(mixed)

Will auto convert any given value to HEX. Number strings will be interpreted as numbers. Text strings will be interpreted as UTF-8 strings.

Parameters

  1. mixed - String|Number|BN|BigNumber: The input to convert to HEX.

Returns

String: The resulting HEX string.

Example

web3.utils.toHex('234');
> "0xea"

web3.utils.toHex(234);
> "0xea"

web3.utils.toHex(new BN('234'));
> "0xea"

web3.utils.toHex(new BigNumber('234'));
> "0xea"

web3.utils.toHex('I have 100€');
> "0x49206861766520313030e282ac"

stripHexPrefix

Returns provided string without 0x prefix.

Parameters

  1. str - string: Input string

Returns

String: The input string without 0x prefix.

Example

web3.utils.stripHexPrefix('234');
> "234"

web3.utils.stripHexPrefix('0x234');
> "234"

web3.utils.stripHexPrefix(42);
> 42

toBN

web3.utils.toBN(number)

Will safely convert any given value (including BigNumber.js instances) into a BN.js instance, for handling big numbers in JavaScript.

Note

For just the BN.js class use utils.BN

Parameters

  1. number - String|Number|HEX: Number to convert to a big number.

Returns

Object: The BN.js instance.

Example

web3.utils.toBN(1234).toString();
> "1234"

web3.utils.toBN('1234').add(web3.utils.toBN('1')).toString();
> "1235"

web3.utils.toBN('0xea').toString();
> "234"

hexToNumberString

web3.utils.hexToNumberString(hex)

Returns the number representation of a given HEX value as a string.

Parameters

  1. hexString - String|HEX: A string to hash.

Returns

String: The number as a string.

Example

web3.utils.hexToNumberString('0xea');
> "234"

hexToNumber

web3.utils.hexToNumber(hex)
web3.utils.toDecimal(hex) // ALIAS, deprecated

Returns the number representation of a given HEX value.

Note

This is not useful for big numbers, rather use utils.toBN instead.

Parameters

  1. hexString - String|HEX: A string to hash.

Returns

Number

Example

web3.utils.hexToNumber('0xea');
> 234

numberToHex

web3.utils.numberToHex(number)
web3.utils.fromDecimal(number) // ALIAS, deprecated

Returns the HEX representation of a given number value.

Parameters

  1. number - String|Number|BN|BigNumber: A number as string or number.

Returns

String: The HEX value of the given number.

Example

web3.utils.numberToHex('234');
> '0xea'

hexToUtf8

web3.utils.hexToUtf8(hex)
web3.utils.hexToString(hex) // ALIAS
web3.utils.toUtf8(hex) // ALIAS, deprecated

Returns the UTF-8 string representation of a given HEX value.

Parameters

  1. hex - String: A HEX string to convert to a UTF-8 string.

Returns

String: The UTF-8 string.

Example

web3.utils.hexToUtf8('0x49206861766520313030e282ac');
> "I have 100€"

hexToAscii

web3.utils.hexToAscii(hex)
web3.utils.toAscii(hex) // ALIAS, deprecated

Returns the ASCII string representation of a given HEX value.

Parameters

  1. hex - String: A HEX string to convert to an ASCII string.

Returns

String: The ASCII string.

Example

web3.utils.hexToAscii('0x4920686176652031303021');
> "I have 100!"

utf8ToHex

web3.utils.utf8ToHex(string)
web3.utils.stringToHex(string) // ALIAS
web3.utils.fromUtf8(string) // ALIAS, deprecated

Returns the HEX representation of a given UTF-8 string.

Parameters

  1. string - String: A UTF-8 string to convert to a HEX string.

Returns

String: The HEX string.

Example

web3.utils.utf8ToHex('I have 100€');
> "0x49206861766520313030e282ac"

asciiToHex

web3.utils.asciiToHex(string)
web3.utils.fromAscii(string) // ALIAS, deprecated

Returns the HEX representation of a given ASCII string.

Parameters

  1. string - String: An ASCII string to convert to a HEX string.

Returns

String: The HEX string.

Example

web3.utils.asciiToHex('I have 100!');
> "0x4920686176652031303021"

hexToBytes

web3.utils.hexToBytes(hex)

Returns a byte array from the given HEX string.

Parameters

  1. hex - String|HEX: A HEX to convert.

Returns

Array: The byte array.

Example

web3.utils.hexToBytes('0x000000ea');
> [ 0, 0, 0, 234 ]

web3.utils.hexToBytes(0x000000ea);
> [ 234 ]

bytesToHex

web3.utils.bytesToHex(byteArray)

Returns a HEX string from a byte array.

Parameters

  1. byteArray - Array: A byte array to convert.

Returns

String: The HEX string.

Example

web3.utils.bytesToHex([ 72, 101, 108, 108, 111, 33, 36 ]);
> "0x48656c6c6f2125"

toWei

web3.utils.toWei(number [, unit])

Converts any ether value value into wei.

Note

“wei” are the smallest ether unit, and you should always make calculations in wei and convert only for display reasons.

Parameters

  1. number - String|BN: The value.
  2. unit - String (optional, defaults to "ether"): The ether to convert from. Possible units are:
    • noether: ‘0’
    • wei: ‘1’
    • kwei: ‘1000’
    • Kwei: ‘1000’
    • babbage: ‘1000’
    • femtoether: ‘1000’
    • mwei: ‘1000000’
    • Mwei: ‘1000000’
    • lovelace: ‘1000000’
    • picoether: ‘1000000’
    • gwei: ‘1000000000’
    • Gwei: ‘1000000000’
    • shannon: ‘1000000000’
    • nanoether: ‘1000000000’
    • nano: ‘1000000000’
    • szabo: ‘1000000000000’
    • microether: ‘1000000000000’
    • micro: ‘1000000000000’
    • finney: ‘1000000000000000’
    • milliether: ‘1000000000000000’
    • milli: ‘1000000000000000’
    • ether: ‘1000000000000000000’
    • kether: ‘1000000000000000000000’
    • grand: ‘1000000000000000000000’
    • mether: ‘1000000000000000000000000’
    • gether: ‘1000000000000000000000000000’
    • tether: ‘1000000000000000000000000000000’

Returns

String|BN: If a string is given it returns a number string, otherwise a BN.js instance.

Example

web3.utils.toWei('1', 'ether');
> "1000000000000000000"

web3.utils.toWei('1', 'finney');
> "1000000000000000"

web3.utils.toWei('1', 'szabo');
> "1000000000000"

web3.utils.toWei('1', 'shannon');
> "1000000000"

fromWei

web3.utils.fromWei(number [, unit])

Converts any wei value into an ether value.

Note

“wei” are the smallest ether unit, and you should always make calculations in wei and convert only for display reasons.

Parameters

  1. number - String|BN: The value in wei.
  2. unit - String (optional, defaults to "ether"): The ether to convert to. Possible units are:
    • noether: ‘0’
    • wei: ‘1’
    • kwei: ‘1000’
    • Kwei: ‘1000’
    • babbage: ‘1000’
    • femtoether: ‘1000’
    • mwei: ‘1000000’
    • Mwei: ‘1000000’
    • lovelace: ‘1000000’
    • picoether: ‘1000000’
    • gwei: ‘1000000000’
    • Gwei: ‘1000000000’
    • shannon: ‘1000000000’
    • nanoether: ‘1000000000’
    • nano: ‘1000000000’
    • szabo: ‘1000000000000’
    • microether: ‘1000000000000’
    • micro: ‘1000000000000’
    • finney: ‘1000000000000000’
    • milliether: ‘1000000000000000’
    • milli: ‘1000000000000000’
    • ether: ‘1000000000000000000’
    • kether: ‘1000000000000000000000’
    • grand: ‘1000000000000000000000’
    • mether: ‘1000000000000000000000000’
    • gether: ‘1000000000000000000000000000’
    • tether: ‘1000000000000000000000000000000’

Returns

String: It always returns a string number.

Example

web3.utils.fromWei('1', 'ether');
> "0.000000000000000001"

web3.utils.fromWei('1', 'finney');
> "0.000000000000001"

web3.utils.fromWei('1', 'szabo');
> "0.000000000001"

web3.utils.fromWei('1', 'shannon');
> "0.000000001"

unitMap

web3.utils.unitMap

Shows all possible ether value and their amount in wei.

Return value

  • Object with the following properties:
    • noether: ‘0’
    • wei: ‘1’
    • kwei: ‘1000’
    • Kwei: ‘1000’
    • babbage: ‘1000’
    • femtoether: ‘1000’
    • mwei: ‘1000000’
    • Mwei: ‘1000000’
    • lovelace: ‘1000000’
    • picoether: ‘1000000’
    • gwei: ‘1000000000’
    • Gwei: ‘1000000000’
    • shannon: ‘1000000000’
    • nanoether: ‘1000000000’
    • nano: ‘1000000000’
    • szabo: ‘1000000000000’
    • microether: ‘1000000000000’
    • micro: ‘1000000000000’
    • finney: ‘1000000000000000’
    • milliether: ‘1000000000000000’
    • milli: ‘1000000000000000’
    • ether: ‘1000000000000000000’
    • kether: ‘1000000000000000000000’
    • grand: ‘1000000000000000000000’
    • mether: ‘1000000000000000000000000’
    • gether: ‘1000000000000000000000000000’
    • tether: ‘1000000000000000000000000000000’

Example

web3.utils.unitMap
> {
    noether: '0',
    wei:        '1',
    kwei:       '1000',
    Kwei:       '1000',
    babbage:    '1000',
    femtoether: '1000',
    mwei:       '1000000',
    Mwei:       '1000000',
    lovelace:   '1000000',
    picoether:  '1000000',
    gwei:       '1000000000',
    Gwei:       '1000000000',
    shannon:    '1000000000',
    nanoether:  '1000000000',
    nano:       '1000000000',
    szabo:      '1000000000000',
    microether: '1000000000000',
    micro:      '1000000000000',
    finney:     '1000000000000000',
    milliether: '1000000000000000',
    milli:      '1000000000000000',
    ether:      '1000000000000000000',
    kether:     '1000000000000000000000',
    grand:      '1000000000000000000000',
    mether:     '1000000000000000000000000',
    gether:     '1000000000000000000000000000',
    tether:     '1000000000000000000000000000000'
}

padLeft

web3.utils.padLeft(string, characterAmount [, sign])
web3.utils.leftPad(string, characterAmount [, sign]) // ALIAS

Adds a padding on the left of a string, Useful for adding paddings to HEX strings.

Parameters

  1. string - String: The string to add padding on the left.
  2. characterAmount - Number: The number of characters the total string should have.
  3. sign - String (optional): The character sign to use, defaults to "0".

Returns

String: The padded string.

Example

web3.utils.padLeft('0x3456ff', 20);
> "0x000000000000003456ff"

web3.utils.padLeft(0x3456ff, 20);
> "0x000000000000003456ff"

web3.utils.padLeft('Hello', 20, 'x');
> "xxxxxxxxxxxxxxxHello"

padRight

web3.utils.padRight(string, characterAmount [, sign])
web3.utils.rightPad(string, characterAmount [, sign]) // ALIAS

Adds a padding on the right of a string, Useful for adding paddings to HEX strings.

Parameters

  1. string - String: The string to add padding on the right.
  2. characterAmount - Number: The number of characters the total string should have.
  3. sign - String (optional): The character sign to use, defaults to "0".

Returns

String: The padded string.

Example

web3.utils.padRight('0x3456ff', 20);
> "0x3456ff00000000000000"

web3.utils.padRight(0x3456ff, 20);
> "0x3456ff00000000000000"

web3.utils.padRight('Hello', 20, 'x');
> "Helloxxxxxxxxxxxxxxx"

toTwosComplement

web3.utils.toTwosComplement(number)

Converts a negative number into a two’s complement.

Parameters

  1. number - Number|String|BigNumber: The number to convert.

Returns

String: The converted hex string.

Example

web3.utils.toTwosComplement('-1');
> "0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"

web3.utils.toTwosComplement(-1);
> "0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"

web3.utils.toTwosComplement('0x1');
> "0x0000000000000000000000000000000000000000000000000000000000000001"

web3.utils.toTwosComplement(-15);
> "0xfffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff1"

web3.utils.toTwosComplement('-0x1');
> "0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"