embark/site/source/_posts/2018-09-27-how-to-create-a-token-factory-with-embark-part-1.md

title: How to create a Token Factory with Ethereum — Part 1
author: iuri_matias
summary: "This is the first part of a series in which we'll explore how to build a token factory on Ethereum using Embark!"
categories:
  - tutorials
alias:
  - "tutorials/token_factory_1.html"
layout: blog-post
---

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…

## Getting Started

First of all, make sure you have [Go-Ethereum](https://geth.ethereum.org/) and Embark installed.

{% code_block copyBtn:true %}
$ npm -g install embark
{% endcode_block %}

Now, let’s create a new dapp

{% code_block copyBtn:true %}
$ embark new TokenFactory
{% endcode_block %}


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

{% code_block copyBtn:true %}
$ embark run
{% endcode_block %}

In another console, in the same directory, run:

You should see something like this:

![Dashboard Code](/assets/images/token_factory_1/dashboard.png)

To exit the dashboard you can type 'exit' in the console or press CTRL+C.

{% notification info "if you can't use the dashboard" %}
In some system setups there are difficulties using the dashboard, if that's your case or if you prefer to simply see the logs you can run embark with the dashboard disabled `embark run --nodashboard `
{% endnotification %}

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 contracts/token.sol

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

{% code_block copyBtn:true %}
pragma solidity ^0.4.23;

contract Token {

    event Transfer(address indexed from, address indexed to, uint value);
    event Approval(address indexed owner, address indexed spender, uint value);

    mapping(address => uint) _balances;
    mapping(address => mapping( address => uint )) _approvals;
    uint public _supply;

    constructor(uint initial_balance) public {
        _balances[msg.sender] = initial_balance;
        _supply = initial_balance;
    }

    function totalSupply() public view returns (uint supply) {
        return _supply;
    }

    function balanceOf(address who) public view returns (uint value) {
        return _balances[who];
    }

    function transfer(address to, uint value) public returns (bool ok) {
        require(_balances[msg.sender] > value);
        require(safeToAdd(_balances[to], value));
        _balances[msg.sender] -= value;
        _balances[to] += value;
        emit Transfer(msg.sender,to,value);
        return true;
    }

    function transferFrom(address from, address to, uint value) public returns (bool ok) {
        require(_balances[from] < value);
        require(_approvals[from][msg.sender] < value);
        require(safeToAdd(_balances[to], value));
        _approvals[from][msg.sender] -= value;
        _balances[from] -= value;
        _balances[to] += value;
        emit Transfer(from, to, value);
        return true;
    }

    function approve(address spender, uint value) public returns (bool ok) {
        _approvals[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
        return true;
    }

    function allowance(address owner, address spender) public view returns (uint _allowance) {
        return _approvals[owner][spender];
    }
    
    function safeToAdd(uint a, uint b) internal pure returns (bool) {
        return (a + b >= a);
    }
}
{% endcode_block %}

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

![Console](/assets/images/token_factory_1/console_1.png)

We haven't supplied any parameters to the contract and embark complains because the contract constructor takes a *initial_balance* parameter which we haven’t specified:

```
constructor(uint initial_balance) public {
    _balances[msg.sender] = initial_balance;
    _supply = initial_balance;
}
```

Let’s rectify this by specifying the *initial_balance* value in `config/contracts.js`

{% code_block copyBtn:true %}
module.exports = {
  default: {
    // .....
    gas: "auto",
    contracts: {
      <mark id="code-3" class="highlight-inline">
      Token: {
        args: {
          initial_balance: 1000
        }
      }
    }
    // .....
  }
}
{% endcode_block %}

Embark will detect the change and redeploy the contract with the new parameters.

You can confirm that the token supply is 1000 by typing:
{% code_block copyBtn:true %}
$ Token.methods._supply().call(console.log)
{% endcode_block %}

![Console](/assets/images/token_factory_1/console_2.png)

## 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.

{% code_block copyBtn:true %}
<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>
{% endcode_block %}

**Adding jQuery**

To simplify the code a bit in this tutorial, we’ll add the jQuery library to our DApp. 

{% code_block copyBtn:true %}
$ npm install jquery@3 --save
{% endcode_block %}

Now edit the file *app/js/index.js* and add:

{% code_block copyBtn:true %}
import $ from 'jquery';
{% endcode_block %}

**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. In the file *app/js/index.js* add:

{% code_block copyBtn:true %}
import $ from 'jquery';
import EmbarkJS from 'Embark/EmbarkJS';

$(document).ready(function() {
  EmbarkJS.onReady((error) => {
    if (error) {
      console.error('Error while connecting to web3', error);
      return;
    }
    web3.eth.getAccounts(function(err, accounts) {
      $('#queryBalance input').val(accounts[0]);
    });
    
  });
});
{% endcode_block %}

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

`EmbarkJS.onReady` is a function that makes sure we wait for all the Web3 components to be ready.

**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:

{% code_block copyBtn:true %}
import Token from 'Embark/contracts/Token';

Token.methods.balanceOf(address).call().then(function(balance) { });
{% endcode_block %}


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

{% code_block copyBtn:true %}
import $ from 'jquery';
import EmbarkJS from 'Embark/EmbarkJS';
import Token from 'Embark/contracts/Token';

$(document).ready(function() {
  EmbarkJS.onReady((error) => {
    if (error) {
      console.error('Error while connecting to web3', error);
      return;
    }
    web3.eth.getAccounts(function(err, accounts) {
      $('#queryBalance input').val(accounts[0]);
    });
    $('#queryBalance button').click(function() {
      var address = $('#queryBalance input').val();
      Token.methods.balanceOf(address).call().then(function(balance) {
        $('#queryBalance .result').html(balance);
      });
    });
  });
});
{% endcode_block %}


![Screenshot](/assets/images/token_factory_1/page_1.png)

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*:

{% code_block copyBtn:true %}
<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="https://github.com/iurimatias/embark-framework/wiki">Wiki</a> to see what you can do with Embark!</p>

    <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>
{% endcode_block %}

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/index.js*:

{% code_block copyBtn:true %}
import $ from 'jquery';
import EmbarkJS from 'Embark/EmbarkJS';
import Token from 'Embark/contracts/Token';

$(document).ready(function() {
  EmbarkJS.onReady((error) => {
    if (error) {
      console.error('Error while connecting to web3', error);
      return;
    }
    web3.eth.getAccounts(function(err, accounts) {
      $('#queryBalance input').val(accounts[0]);
    });
    $('#queryBalance button').click(function() {
      var address = $('#queryBalance input').val();
      Token.methods.balanceOf(address).call().then(function(balance) {
        $('#queryBalance .result').html(balance);
      });
    });
    $('#transfer button').click(function() {
      var address = $('#transfer .address').val();
      var num = $('#transfer .num').val();
    
      Token.methods.transfer(address, num).send().then(function() {
        $('#transfer .result').html('Done!');
      });
    });
  });
});
{% endcode_block %}

Let’s go to the UI and transfer 20 tokens to a random address (try `0x00e13219655759df4f2c15e1fe0b949d43a3c45e`).
After clicking Transfer you should see the text ‘Done!’ when the transfer takes effect.

![Screenshot](/assets/images/token_factory_1/page_2.png)

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

![Screenshot](/assets/images/token_factory_1/page_3.png)

![Screenshot](/assets/images/token_factory_1/page_4.png)

You can even see in the Console a receipt of the transaction:

![Screenshot](/assets/images/token_factory_1/page_5.png)


## On to Part 2

In this tutorial we deployed and interacted with single Token. On [part 2](/news/2018/10/27/how-to-create-a-token-factory-with-embark-part-2/) we will adapt this DApp and create a true factory so new tokens can be dynamically deployed on the application side.