How it works

• ethereum.js
• providers:
  • qt
  • http
  • websockets
• cpp / go implementation
• jsonrpc server
• connectors:
  • qt
  • http
  • websockets

• ethereum.js
• providers:
  • qt
  • http
  • websockets
• cpp / go implementation
• jsonrpc server
• connectors:
  • qt
  • http
  • websockets

Get coinbase

• javascript code

  web3.eth.coinbase.then(function (result) {
  	var coinbase = result;
  });

• json object

  {
  	"jsonrpc" : "2.0",
  	"method" : "eth_coinbase",
  	"params" : null,
  	"id" : 1
  }	
  								

• curl request

  curl -X POST --data '{"jsonrpc":"2.0","method":"eth_number","params":null,"id":1}' http://localhost:8080

Why promises?

Callback hell

Callback hell

asyncCall(function (result) {
    // do something 

    anotherAsyncCall(function (result2) {
        // do something 2

        oneMoreAsyncCall(function (err, result3) {
            // the third and final async response

            if (err) {
                //handle any error resulting from any of the above calls	

                return; // finally!
            }
        })
    })
})

Promises

asyncCall()
.then(function(data1){
    // do something...
    return anotherAsyncCall();
})
.then(function(data2){
    // do something...  
    return oneMoreAsyncCall();    
})
.then(function(data3){
   // the third and final async response
})
.fail(function(err) {
   // handle any error resulting from any of the above calls    
})
.done();

Example

web3.eth.coinbase.then(function (result) {
	var coinbase = result;
	console.log(coinbase); // "0x407d73d8a49eeb85d32cf465507dd71d507100c1"
	return web3.eth.balanceAt(coinbase);
}).then(function (result) {
	var balance = result;
	console.log(balance); // "0x32884442997a37a000"
});

Improved Example

web3.eth.balanceAt(web3.eth.coinbase).then(function (result) {
	var balance = result;
	console.log(balance); // "0x32884442997a37a000"
});

Autoresolving promises

web3.eth.somemethod(x).then(function (result) {
	// some code
});

var x = {
	"a" : "text",
	"b" : Promise,
	"c" : 7,
	"d" : Promise
}

var x = {
	"a" : "text",
	"b" : "Hello World!",
	"c" : 7,
	"d" : ["Hello", "World", Promise]
}

var x = {
	"a" : "text",
	"b" : "Hello World!",
	"c" : 7,
	"d" : ["Hello", "World", 14]
}

Contracts

Contract creation

var source = "" + 
"contract test {" +
"   function multiply(uint a) returns(uint d) {" +
"       return a * 7;" +
"   }" +
"}";

// create contract
web3.eth.transact({code: web3.eth.solidity(source)}).then(function (address) {
	// ...
});

Contract object

var desc =  [{
    "name": "multiply",
    "inputs": [{
        "name": "a",
        "type": "uint256"
    }],
    "outputs": [{
        "name": "d",
        "type": "uint256"
    }]
}];

// create description
var account = "0x407d73d8a49eeb85d32cf465507dd71d507100c1"; // 
var contract = web3.contract(account, desc); // create contract object here!

contract.multiply(1).call().then(function(res) {
	var result = res[0];
	console.log(result); // 7
});