The json interface is a json object describing the Application Binary Interface (ABI) for a 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:

1. type: "function", "constructor" (can be omitted, defaulting to "function"; "fallback" also possible but not relevant in web3.js).

2. name: the name of the function (only present for function types).

3. constant: true if function is specified to not modify the blockchain state.

4. payable: true if function accepts ether, defaults to false

5. stateMutability: a string with one of the following values:

   1. pure (specified to not read blockchain state)

   2. view (same as constant above)

   3. nonpayable and payable (same as payable above)

6. inputs: an array of objects, each of which contains:

   1. name: the name of the parameter

   2. type: the canonical type of the parameter

7. outputs: an array of objects same as inputs, can be omitted if no outputs exist.

Events:

1. type: always "event"

2. name: the name of the event.

3. inputs: an array of objects, each of which contains:

   1. name: the name of the parameter.

   2. type: the canonical type of the parameter.

   3. indexed: true if the field is part of the log's topics, false if it one of the log's data segment.

4. 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
    }]