Outdated: New tutorial can be found on the embark website

(Disclaimer: this tutorial is for educational purposes only)

In this tutorial series we’ll create a Token Factory using Ethereum. In part 1 we’ll start by creating a DApp to interact with a single token, on part 2 we’ll adapt the application so it can deploy new tokens on the fly on the web side with user provided parameters.

A Token is typically a unit used to represent a medium of exchange for some service or utility. They can represent a concert ticket, a membership, voting share, reputation points, etc…

note: This tutorial is meant for embark 2.5.2 (not 2.6.0 and above)

Getting Started

First of all, make sure you have Go-Ethereum and Embark installed.

npm -g install embark@2.5.2

Now, let’s create a new dapp

embark new TokenFactory

This will create a directory called TokenFactory, cd to it and run:

embark blockchain

In another console, in the same directory, run:

embark run

You should see something like this:

note: If you don’t want the console you can instead run:

embark run — nodashboard

Now open your browser at http://localhost:8000 , start your favourite editor and let’s get started!

Adding the Token Contract

We’ll add a typical ERC20 token contract to app/contracts/token.sol

warning: this contract is for educational purposes only, do not use it in production unless you know what you are doing

Embark will automatically detect the new file and deploy the contract. However we quickly notice a problem, in Embark’s console type:

Token._supply().toNumber()

The supply is zero, that’s because the contract constructor takes a initial_balance parameter which we haven’t specified:

function Token( uint initial_balance ) {

_balances[msg.sender] = initial_balance;

_supply = initial_balance;

}

Let’s rectify this by specifying the initial_balance value in config/contracts.json

{

"default": {

"gas": "auto",

"contracts": {

"Token": {

"args": [

1000

]

}

}

}

}

Embark will detect the change and redeploy the contract with the new parameters, afterwards the token supply is 1000 as expected:

Creating the UI

For the sake of brevity, we wouldn’t implement every single functionality in the contract. However, we’ll implement two important features: Checking balance of an address and Transferring Tokens from one address to another.

Checking address balance

To input the address to query, we’ll edit app/index.html and add a simple form.

<html>

<head>

<title>Embark</title>

<link rel="stylesheet" href="css/app.css">

<script src="js/app.js"></script>

</head>

<body>



<div id="queryBalance">

<h3>Query Balance</h3>

<input placeholder="enter account address: e.g 0x123" />

<button>Query</button>

<div class="result"></div>

</div> </body>

</html>

Adding jQuery

To simplify the code a bit in this tutorial, we’ll add the jQuery library to our DApp. Download jQuery from here and save it in your dapp app/js/ folder. Alternatively:

note: To use libraries such as react, give a look at a plugin such as embark-babel

Setting the default address

Let’s add to the input field field our own address as the default text so we can easily query our own balance. create the file app/js/token.js and add:

$(document).ready(function() { web3.eth.getAccounts(function(err, accounts) {

$('#queryBalance input').val(accounts[0]);

}); });

This will get the address of the first account and set it as the default text in the input form.

Querying Balance

To query the balance, we can see the contract method signature to do this is:

function balanceOf( address who ) constant returns (uint value) {

return _balances[who];

}

This method will be available in the JS code automatically as a promise, like:

Token.balanceOf(address).then(function(balance) { });

So we can simply add a click event to the button, get the address, query the balance and set the result.

$(document).ready(function() { web3.eth.getAccounts(function(err, accounts) {

$('#queryBalance input').val(accounts[0]);

}); $('#queryBalance button').click(function() {

var address = $('#queryBalance input').val(); Token.balanceOf(address).then(function(balance) {

$('#queryBalance .result').html(balance.toString());

});

}); });

note: since the balance variable is a Big Integer, to read it it’s necessary to apply either .toNumber() or .toString()

Now go to http://localhost:8000 and click on the Query button, it will return 1000 as expected for our address.

Transferring Tokens

Now let’s implement transferring tokens!

Now checking the contract, this is the method for transferring tokens:

function transfer( address to, uint value) returns (bool ok)

The method will take two parameters, an address and a value. Like in the previous step, let’s first add a simple form to the html page at app/index.html:



<head>

<title>Embark</title>

<link rel="stylesheet" href="css/app.css">

<script src="js/app.js"></script>

</head>

<body>

<h3>Welcome to Embark!</h3>

<p>See the <a href=" Embark Welcome to Embark! See the https://github.com/iurimatias/embark-framework/wiki ">Wiki to see what you can do with Embark! <div id="queryBalance">

<h3>Query Balance</h3>

<input placeholder="enter account address: e.g 0x123" />

<button>Query</button>

<div class="result"></div>

</div> <div id="transfer">

<h3>Transfer Tokens</h3>

<input class="address" placeholder="enter account address: e.g 0x123" />

<input class="num" placeholder="enter amount to transfer" />

<button>Transfer</button>

<div class="result"></div>

</div> </body>

</html>

Then we will add the code to take the address and number of tokens from the inputs and call the contracts transfer method to app/js/token.js

$(document).ready(function() { web3.eth.getAccounts(function(err, accounts) {

$('#queryBalance input').val(accounts[0]);

}); $('#queryBalance button').click(function() {

var address = $('#queryBalance input').val(); Token.balanceOf(address).then(function(balance) {

$('#queryBalance .result').html(balance.toString());

});

}); $('#transfer button').click(function() {

var address = $('#transfer .address').val();

var num = $('#transfer .num').val(); Token.transfer(address, num).then(function() {

$('#transfer .result').html('Done!');

});;

}); });

Let’s go to the UI and transfer 20 tokens to a random address, after clicking Transfer you should see the text ‘Done!’ when the transfer takes effect.

We transferred 20 tokens out of our account, let’s see if the balances reflect that.

On to Part 2

In this tutorial we deployed and interacted with single Token. On part 2 we will adapt this DApp and create a true factory so new tokens can be dynamically deployed on the application side.

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