How To Develop a DApp on VeChain (III): Components & Coding
Congratulations! You have made to the last episode of this tutorial. Here we will put everything we know together and make a useful program: a VTHO token transfer tool. The official Sync only provides the VET transfer functionality, our VTHO tools is a very good supplement to the status quo.
Make sure you have the following things ready:
- Sync set up and running on your computer.
- A testing account, which is already presented in Sync.
- Some VET and VTHO in your testing account.
- Sync running on test net.
If you don’t know how above requirements are done, check the previous episode: https://medium.com/@laalaguer/how-to-develop-a-dapp-on-vechain-ii-setup-walk-around-109a01bf7ae9
Setup in 3 minutes
> mkdir vtho-transfer
> cd vtho-transfer/> npm install -g @vue/cli # Install vue-cli.
> vue create -b -n my-project # Create a clean Vue project.> cd my-project # Now you are in a Vue workspace!> npm install vue bootstrap-vue bootstrap # Install BootstrapVue.> npm install bignumber.js # Math library.> npm run serve # Start development server on background.
We are all set! Now let us view our precious project in Sync. Open a tab and navigate to http://localhost:8080. It should be like this:
Due to the length of this tutorial, we write one core component and demo the key functions. The rest of the code and a more complicated example can be found at the bottom of this tutorial.
The app must be stylish! Clean up the default main.js and add a BootstrapVue library, quite simple:
Put the component on the radar screen by editing the App.vue:
Great! Now save both the files and refresh the Sync tab, the dummy web page pretty much looks like this now:
Now that we have the skeleton, let’s move on to make the functions to make the app alive. Create a separate empty file alongside the main.js, name it operations.js, then put several functions into it.
Query the VTHO Balance
Okay, let us first create a function queries the VTHO balance from the VTHO contract on test net, actually, it can be used to query any contract that is VIP180 compatible. It should be like this:
Quite self-explanatory, this
getTokenBalance function queries the contract about how much token the user holds, when we call it, we feed it with the actual contract address and user’s account address. Notice that we used the
call() function of connex.js, which we introduced in the previous episode.
Sign Transaction and Send VTHO
How to sign the transaction and send it to the other person? Simple, we just use the sign-and-send API embedded in the connex.js. Let’s create a function for that, too. Still, in the operation.js, append this code:
The above snippet is mainly about
transferToken , which is a general purpose transfer action. It takes the contract address, sender address, receiver address, amount of transfer, then asks the connex to sign the transaction and send out!
Now finish the operations.js file with the export section as usual:
In the smart contract, the decimals don’t exist. All numbers are integers. To present the numbers right to the decimal, we power it with 10 times precision. So when we say: 123.456 in human language, it should be presented in:
123.456 * (10 ^ 18) and then send to EVM. And vice versa.
So we need some utilities as a broker to help us with number formatting. Create a new file utils.js and place the following content inside:
Great! All is done, now we put things together and make our app alive!
Put Things Together
Firstly, let’s call the VTHO contract and display our VTHO balance, here is what I did in code:
- Fix in the VTHO smart contract address.
- Fix in my account address. (Generated from the previous episode of tutorials)
- Initialization the VTHO balance query before the component is mounted.
Note: you can always use
setTimeout()to recursively query the balance of your account. 😉
Secondly, we add the function of sending VTHO token transactions to the button, so we can get alert whenever it succeeds or fails.
Great! Now update our template to bind to those data:
Now all the code is finished, make sure you have saved the same:
GitHub repo of all the source code: [GitHub Link]
Test the App
Now let us view our first triumph on the VeChain DApp journey!
On Sync browser, visit http://localhost:8080, then do the following:
- Input a receiver: 0x422D582C08d7965cD5Fefef1572faaA15783f473
- Input the amount: 10 VTHO
- Clicking the little “Transfer” blue button.
Then wait for it…. the magic time! Sync prompts me to unlock my account to send the transaction:
Of course, I input the password correctly, and you can see the transaction details on test net here:
VeForge Explore | VeChain Block Explorer
VeForge Explore is the VeChain block explorer. Explore and find VeChain block, account, transaction, and token transfer…
Finally, our example has finished! Thanks for hard working!
One More Thing
If you are interested, this source code also is available at the GitHub below:
The full VeChain token transfer is more complicated, the GitHub is below:
All episodes of tutorials:
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