Using web3 API with MetaMask

This web page shows examples using web3 methods together with MetaMask.

Information about web3 API: https://github.com/ethereum/wiki/wiki/JavaScript-API
Information about MetaMask: https://metamask.io/
Explore Ethereum Test Network Rinkeby blockchain: https://rinkeby.etherscan.io
Explore Ethereum Main Network blockchain: https://etherscan.io/
MetaMask only support the web3 asynchronous methods (there are a few exceptions), see: https://github.com/MetaMask/faq/blob/master/DEVELOPERS.md
Gitter Ethereum/web3.js, see: https://gitter.im/ethereum/web3.js

How to use

Install Chrome browser: https://www.google.com/chrome/
Install the MetaMask plugin from the Chrome Web Store: https://chrome.google.com/webstore/detail/metamask/nkbihfbeogaeaoehlefnkodbefgpgknn
Setup MetaMask, see YouTube movie: https://www.youtube.com/watch?v=6Gf_kRE4MJU
The examples also works if you have setup a local Ethereum node.
WARNING: RUN THE EXAMPLES AGAINST A TEST NETWORK AND NOT ON THE MAIN ETHEREUM NETWORK
I recommend that you use the Rinkeby Test Network.
For the examples create at least two accounts in MetaMask.
Request some Ether from the Rinkeby GitHub Authenticated Faucet https://faucet.rinkeby.io/
Log in MetaMask and select the correct Test Network (Recommended Rinkeby)

Examples

[web3.eth.defaultAccount] This default account is used for the following methods:
- web3.eth.sendTransaction()
- web3.eth.call()
Note: The defaultAccount optionally can be overwritten by specifying the from property.
Default account (rinkeby example):

[web3.sha3] The Keccak-256 SHA3 of the given data
Data to be hashed:

Encoding:

[web3.toHex] Converts any value into HEX
Data to be converted into hex:

[web3.toAscii] Converts a HEX string into a ASCII string
Hex string:

[web3.fromAscii] Converts any ASCII string to a HEX string.
ASCII string:

The number of bytes the returned HEX string should have (No paddding if value = 0). This does not work!! Bug maybe?

[web3.toDecimal] Converts a HEX string to its number representation.
An HEX string to be converted to a number:

[web3.fromDecimal] Converts a number or number string to its HEX representation.
A number to be converted to a HEX string:

[web3.fromWei] Converts a number of wei into selected ethereum unit:
Wei (in dec or hex):

Unit:

[web3.toWei] Converts an ethereum unit into wei:
Number of Ethereum units (in dec or hex):

Unit:

[web3.toBigNumber] Converts a given number into a BigNumber instance.
A number, number string or HEX string of a number:

[web3.isAddress] Checks if the given string is an address.
An address (HEX string):

[web3.eth.getCode] Get the code at the specified contract address
Contract Address (rinkeby example):

To find the contract address deployed from an address, goto https://rinkeby.etherscan.io enter the address and search for the transaction which created the contract.
In the transaction details you will find the contract address.

[web3.eth.getBlock] Get the block information at the specified block hash or block number
Block hash or block number (rinkeby example):

[web3.eth.getBlockTransactionCount] Get number of transaction at the specified block hash or block number
Block hash or block number (rinkeby example):

[web3.eth.getUncle] Get blocks uncle for given block hash or block number and uncle index position
Block hash or block number (mainnet example):

Uncle index position

[web3.eth.getTransaction] Get transactions for given transaction hash
Transaction hash (rinkeby example):

[web3.eth.getTransactionFromBlock] Get transactions for given block hash or block number and transaction index position
Block hash or block number (rinkeby example):

Transaction index position

[web3.eth.getTransactionReceipt] Get transaction receipt for given transaction hash

Use this method to get the contract address.
When a contract is created using method web3.eth.sendTransaction a transaction hash is returned.
This transaction hash can be used as input for web3.eth.getTransactionReceipt.

Note:
If you got null instead of a receipt the transaction has not been included in a block yet.
Wait for a moment and check if a miner has included the transaction in a block and retry it.

Transaction hash (rinkeby example):

[web3.eth.getTransactionCount] Get the number of transaction send for specified address
Address (rinkeby example):

[web3.eth.sendTransaction] Send a transaction (ether transfer)
From account (rinkeby example):

To account:

Amount (Ether):

[web3.eth.sendTransaction] Send a transaction (contract creation)
From account (rinkeby example):

Bytecode:

Note:
The Bytecode value above was created as follow:

Greeter contract copied from: https://www.ethereum.org/greeter.

pragma solidity ^0.4.0; contract mortal { /* Define variable owner of the type address*/ address owner; /* this function is executed at initialization and sets the owner of the contract */ function mortal() { owner = msg.sender; } /* Function to recover the funds on the contract */ function kill() { if (msg.sender == owner) selfdestruct(owner); } } contract greeter is mortal { /* define variable greeting of the type string */ string greeting; /* this runs when the contract is executed */ function greeter(string _greeting) public { greeting = _greeting; } /* main function */ function greet() constant returns (string) { return greeting; } }
Load this code into the Remix Solidity IDE http://remix.ethereum.org or press this link and it will be done automatically for you (Use Chrome browser).
Compile the code in the Remix Solidity IDE.
Select the Contract tab and click the link "Contract details (bytecode, interface etc.)".
Copy the Remix Bytecode value and paste it into the Bytecode field above.
I already copied the Greeter interface here below, because you will need it in the web3.eth.call example:

[{"constant":false,"inputs":[],"name":"kill","outputs":[],"payable":false,"type":"function"},{"constant":true,"inputs":[],"name":"greet","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function"},{"inputs":[{"name":"_greeting","type":"string"}],"payable":false,"type":"constructor"}]

[web3.eth.sign] Sign data
From a specific account (rinkeby example):

Data to sign: