Note

This documentation is under construction and documents the 2.x alpha versions of web3.js. The current stable version of web3.js is 1.0 and should get preferred for production use cases.

web3.utils

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


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

Returns

Object: The BN.js instance.

Example

const 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: An BN.js instance.

Returns

Boolean

Example

const 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

const number = new BigNumber(10);

web3.utils.isBigNumber(number);
> true

keccak256

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

Will calculate the keccak256 of the input.

Note

To mimic the keccak256 behaviour of solidity use soliditySha3

Parameters

  1. string - String: A string to hash.

Returns

String: the result hash.

Example

web3.utils.keccak256('234'); // taken as string
> "0xc1912fee45d61c87cc5ea59dae311904cd86b84fee17cc96966216f811ce6a79"

web3.utils.keccak256(new BN('234'));
> "0xbc36789e7a1e281436464229828f817d6612f7b477d66591ff96a9e064bcc98a"

web3.utils.keccak256(234);
> null // can't calculate the hash of a number

web3.utils.keccak256(0xea); // same as above, just the HEX representation of the number
> null

web3.utils.keccak256('0xea'); // will be converted to a byte array first, and then hashed
> "0x2f20677459120677484f7104c76deb6846a2c071f9b3152c103bb12cd54d1a4a"

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.

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

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"

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,  [, chainId])

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.
  2. chainId - number (optional): Chain id where checksummed address should be valid, defaults to null. RSKIP-60 <https://github.com/rsksmart/RSKIPs/blob/master/IPs/RSKIP60.md> for details.

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

web3.utils.isAddress('0x5aaEB6053f3e94c9b9a09f33669435E7ef1bEAeD', 30);
> true

toChecksumAddress

web3.utils.toChecksumAddress(address[, chainId])

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

Parameters

  1. address - String: An address string.
  2. chainId - number (optional): Chain id where checksummed address should be valid, defaults to null. RSKIP-60 <https://github.com/rsksmart/RSKIPs/blob/master/IPs/RSKIP60.md> for details.

Returns

String: The checksum address.

Example

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

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

web3.utils.toChecksumAddress('0x5aaeb6053f3e94c9b9a09f33669435e7ef1beaed', 30);
> "0x5aaEB6053f3e94c9b9a09f33669435E7ef1bEAeD"

stripHexPrefix

Removes the prefix 0x from a given hex if it exists.

Parameters

  1. hex - String: Hex

Returns

String: Hex without prefix.

Example


checkAddressChecksum

web3.utils.checkAddressChecksum(address [, chainId])

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

Parameters

  1. address - String: An address string.
  2. chainId - number (optional): Chain id where checksummed address should be valid, defaults to null. RSKIP-60 <https://github.com/rsksmart/RSKIPs/blob/master/IPs/RSKIP60.md> for details.

Returns

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

Example

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

web3.utils.checkAddressChecksum('0x5aAeb6053F3e94c9b9A09F33669435E7EF1BEaEd', 31);
> true

toHex

web3.utils.toHex(mixed)

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

Parameters

  1. value - 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"

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 a 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. If you would like to transform an ASCII string into a valid bytes4, bytes8 etc. value then please pass the correct length as the second parameter.

Parameters

  1. string - String: A ASCII string to convert to a HEX string.
  2. length - Number: The length of the returned hex string. The default size is 32 e.g.: bytes32.

Returns

String: The HEX string.

Example

web3.utils.asciiToHex('I have 100!');
> "0x4920686176652031303021000000000000000000000000000000000000000000"

// transforming to a bytes4 value:
web3.utils.asciiToHex('yes', 4);

// transforming to a bytes8 value:
web3.utils.asciiToHex('yes', 8);

//etc.

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 ethere 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 a ether value.

Note

“wei” are the smallest ethere 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 numer 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"

getSignatureParameters

web3.utils.getSignatureParameters(string)

Gets the r, s and v values of an ECDSA signature

Parameters

  1. string - String: An ECDSA signature.

Returns

Object: Object containing r,s,v values.

Example

web3.utils.getSignatureParameters('0x5763ab346198e3e6cc4d53996ccdeca0c941cb6cb70d671d97711c421d3bf7922c77ef244ad40e5262d1721bf9638fb06bab8ed3c43bfaa80d6da0be9bbd33dc1b');
> "{ r: '0x5763ab346198e3e6cc4d53996ccdeca0c941cb6cb70d671d97711c421d3bf792', s: '0x2c77ef244ad40e5262d1721bf9638fb06bab8ed3c43bfaa80d6da0be9bbd33dc', v: 27 }"