Note

This documentation is work in progress and web3.js 1.0 is not yet released! You can find the current documentation for web3 0.x.x at github.com/ethereum/wiki/wiki/JavaScript-API.

Glossary


json interface

The json interface is a json object describing the Application Binary Interface (ABI) for an Ethereum smart contract.

Using this json interface web3.js is able to create JavaScript object representing the smart contract and its methods and events using the web3.eth.Contract object.

Specification

Functions:

  • type: "function", "constructor" (can be omitted, defaulting to "function"; "fallback" also possible but not relevant in web3.js);
  • name: the name of the function (only present for function types);
  • constant: true if function is specified to not modify the blockchain state;
  • payable: true if function accepts ether, defaults to false;
  • stateMutability: a string with one of the following values: pure (specified to not read blockchain state), view (same as constant above), nonpayable and payable (same as payable above);
  • inputs: an array of objects, each of which contains:
    • name: the name of the parameter;
    • type: the canonical type of the parameter.
  • outputs: an array of objects same as inputs, can be omitted if no outputs exist.

Events:

  • type: always "event"
  • name: the name of the event;
  • inputs: an array of objects, each of which contains:
    • name: the name of the parameter;
    • type: the canonical type of the parameter.
    • indexed: true if the field is part of the log’s topics, false if it one of the log’s data segment.
  • anonymous: true if the event was declared as anonymous.

Example

contract Test {
    uint a;
    address d = 0x12345678901234567890123456789012;

    function Test(uint testInt)  { a = testInt;}

    event Event(uint indexed b, bytes32 c);

    event Event2(uint indexed b, bytes32 c);

    function foo(uint b, bytes32 c) returns(address) {
        Event(b, c);
        return d;
    }
}

// would result in the JSON:
[{
    "type":"constructor",
    "payable":false,
    "stateMutability":"nonpayable"
    "inputs":[{"name":"testInt","type":"uint256"}],
  },{
    "type":"function",
    "name":"foo",
    "constant":false,
    "payable":false,
    "stateMutability":"nonpayable",
    "inputs":[{"name":"b","type":"uint256"}, {"name":"c","type":"bytes32"}],
    "outputs":[{"name":"","type":"address"}]
  },{
    "type":"event",
    "name":"Event",
    "inputs":[{"indexed":true,"name":"b","type":"uint256"}, {"indexed":false,"name":"c","type":"bytes32"}],
    "anonymous":false
  },{
    "type":"event",
    "name":"Event2",
    "inputs":[{"indexed":true,"name":"b","type":"uint256"},{"indexed":false,"name":"c","type":"bytes32"}],
    "anonymous":false
}]