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 a JavaScript object representing the smart contract , 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), "non-payable" 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 is one of the log’s data segment.

  • anonymous: true if the event was declared as anonymous.

Example

Solidity Contract

pragma solidity ^0.8.4;

contract Test {
	uint256 a;
	address d = 0xdCad3a6d3569DF655070DEd06cb7A1b2Ccd1D3AF;

	constructor(uint256 testInt) {
		a = testInt;
	}

	event Event(uint256 indexed b, bytes32 c);

	event Event2(uint256 indexed b, bytes32 c);

	function foo(uint256 b, bytes32 c) public returns (address) {
		emit Event(b, c);
		return d;
	}
}

Resulting JSON ABI

[
    {
        "type": "constructor",
        "stateMutability": "nonpayable",
        "inputs": [{"internalType":"uint256","name":"testInt","type":"uint256"}],
    },
    {
        "type": "event",
        "name": "Event",
        "inputs": [{"indexed":true,"internalType":"uint256","name":"b","type":"uint256"},{"indexed":false,"internalType":"bytes32","name":"c","type":"bytes32"}],
        "anonymous": false,
    },
    {
        "type": "event",
        "name": "Event2",
        "inputs": [{"indexed":true,"internalType":"uint256","name":"b","type":"uint256"},{"indexed":false,"internalType":"bytes32","name":"c","type":"bytes32"}],
        "anonymous": false,
    },
    {
        "type": "function",
        "name": "foo",
        "stateMutability": "nonpayable",
        "inputs": [{"internalType":"uint256","name":"b","type":"uint256"},{"internalType":"bytes32","name":"c","type":"bytes32"}],
        "outputs": [{"internalType":"address","name":"","type":"address"}],
    }
]