How to encode and decode ABI data?

Can someone show me an example with web3js library?

  • Are you talking about decoding the input and output of a call to a contract? Oe the contract itself? If the former, why? web3 will provide you with stub methods that let you call contract methods without having to do this yourself. – Nick Johnson Apr 26 '16 at 14:05

If the question is about abi params, you can take a look at these two web3.js files:

https://github.com/ethereum/web3.js/blob/master/test/coder.encodeParam.js https://github.com/ethereum/web3.js/blob/master/test/coder.decodeParam.js

Although these functions are not a part of public web3.js interface. Mostly because they need a proper refactor.

There is also a command line tool created especially for encoding function calls and retrieving output data.



In case you need an online tool to encode parameters to abi format you can use https://abi.hashex.org/. It has functionality to auto parse contract's abi to get function names and parameter types and provides convenient way to enter their values.

Here is an example of using this service enter image description here


web3 1.0:

web3.eth.abi.decodeParameter('address', '0000000000000000000000001829d79cce6aa43d13e67216b355e81a7fffb220')

you should receive: 0x1829D79cCE6aA43D13E67216b355E81A7FfFB220

you can also try:




I modified web3 npm library by including the following line

Web3.SolidityCoder = require('./lib/solidity/coder');

after the Web3 object gets created.

In the client side, you can use it with following code.

web3 = require('web3'); // This will import the web3 library.

web3.SolidityCoder.encodeParams([types array], [values array])
web3.SolidityCoder.decodeParams([types array], encodedData)

This of course is a hack and is suitable for quick testing, if this would be a recommended approach, I could push changes to official web3 library. I'll check with them.

Update: There is a getData() method available in web3.js which you can use for this purpose. Here is the link to documentation: https://github.com/ethereum/wiki/wiki/JavaScript-API#contract-methods


The easiest way to to use "abi-decoder". I forked the repository and created index.html for easy usage.

You can download and use it from: https://github.com/Muhammad-Altabba/abi-decoder (you can later check it at https://github.com/ConsenSys/abi-decoder once they will accept my Pull-Request)

To download and run using NPM:

npm install abi-decoder
bower install abi-decoder

Then download https://github.com/Muhammad-Altabba/abi-decoder/index.html to the same directory. Then open the file "index.html" in browser.

You will get:

enter image description here


If you mean the data for sending a message, a simple way is to encode it like this:

contract = web3.eth.contract(abi).at(cAddr);
payload = contract['transfer'].getData(to, amont);

The payload is just what you want.

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