As a Neo fan with zero coding knowledge, I want to shares my experience of going through the “Developing on Neo” course, in a 3-part blog.

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In this last coding lesson: https://neocourse.mywish.io/lesson/8/, I had to create a “dApp”. This abbreviation stands for “decentralized application” and it is essentially a classic App represented by a smart contract and located on a decentralized network, hence the different denomination. In this case I created a simple calculator that multiplies two numbers.

This post covers the following points:

1. The neon-js repository is a useful and necessary tool for creating calls, transactions and smart contracts on the neo blockchain

2. To design a dApp a smart contract and a frontend are required to be made

3. React is used for the creation of the frontend and allows to see what your program produces

First things first, I used “neon-js” which is a JavaScript Library allowing calls, transactions and smart contract creation. You can find it fairly easily by googling “neon-js github” and look for the “documentation website” as illustrated below:

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Once this is installed, two steps are required to start developing the dApp, “frontend” and “smart contract”. Commencing with the frontend, I first needed to use “react” javascript and create a project template using “create-react.app” (React is a very advanced tool based on the programming language JavaScript. It was developed by Facebook and is used for building user interfaces, also called “frontend”. Basically, thanks to it you will see in your browser what your program produces). While this is actually rather straightforward to do, downloading it takes quite some time.

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https://preview.redd.it/u5u1ri1bxs551.png?width=399&format=png&auto=webp&s=fe461fa06520c9d11fcfb505b0e8bf4d75d3346d

Meanwhile, I started writing the “smart contract”. I kept on using Python as language, and entered the “Main” function which only requires two parameters “operation; args” and one operation “Mul”.

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Then, I moved this contract to “neo-local” in order to compile and deploy the contract on the network. Next step was to open a wallet by using the “COZ” password and enter the “sc help” command. I was now able to see the next procedure to follow.

Two commands are given: either “sc build”, used to compile (compilation here means translating the file from programming language into the format understood by Neo Virtual Machine) the contract into an “awm” file, or “build run” if I want to deploy the contract directly. In this context I used “sc build” and “sc deploy” as I first need this file to be in a awm format.

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I was asked to specify whether this contract uses “storage, dynamic calls and fund”. As this contract does not require any of these, entering “False False False” will fix all three issues. Moreover, by using the Github of “CityOfZion” with this link: https://github.com/CityOfZion/neo-smart-contract-examples/blob/master/docs/contract-parameter-type.md, I was able to enter the right parameter types, in this case (0710 02), and deploy the contract, which should be looking as below:

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https://preview.redd.it/6a2qk8qlxs551.png?width=670&format=png&auto=webp&s=29d1f5ee62755aa43c86ad769d9d2d75aff46ddd

Last step of the “smart contract” requires entering the wallet’s password and copying the “Hash” to save it for later. This is the hash I received:

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https://preview.redd.it/7jtx4z6pxs551.png?width=339&format=png&auto=webp&s=fd24c75121183859cba652c3da7075d60bd87bcb

At this point, my “React” project template was fully-downloaded and I was able to proceed with the “frontend”. I added the “neon-js” library to this project and entered “yarn start”.

In order for this dApp to make the multiply operation, I created two set of table A and B with zero value as default and used “state” to store their value:

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https://preview.redd.it/rjtjghbsxs551.png?width=429&format=png&auto=webp&s=66294afac432ec0567a1de1d1beeda7bfc3c6e84

To make A and B interact, I first had to create a form in which I will enter the data. The detailed process is well-explained in the lesson: https://neocourse.mywish.io/lesson/8/

Here is the final result:

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https://preview.redd.it/k6meh4zuxs551.png?width=168&format=png&auto=webp&s=26c13e5152cdf54d2218f7788e45c9a1d5828bea

It was time to call the smart contract. For reference, by checking this link: https://cityofzion.io/neon-js/docs/en/guides/basic/createscript.html, I was able to know all further steps in order to call the contract. First one, was to connect the “neon-js” library by importing this link: import Neon from ‘@cityofzion/neon-js’.

Eventually, I had to enter this last set of variables and copy the “Hash” that I saved earlier:

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https://preview.redd.it/268bxmuxxs551.png?width=695&format=png&auto=webp&s=5c08eb657a432fa8bf21fa6d741b111a079649bc

Important note: when copying the “Hash”, make sure to remove the “0x” in front of it. Then, I called the script by running “rpc query invokescript”. It is important to also notify it in the library since it is not declared anywhere else in the contract:

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https://preview.redd.it/9uzh02g1ys551.png?width=578&format=png&auto=webp&s=7c32b8f4af44fa2e286fff7c1590132cef7ab0ca

the end result looked like this:

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https://preview.redd.it/f8kq6kl4ys551.png?width=749&format=png&auto=webp&s=e9375445ad18a0c07f65b8040856890c563bcfb0

Finally, I had to test whether the calculating action worked or not by simply connecting to the console below, and input the values to be multiplied. Depending on the well execution of the smart contract, the values should be able to multiply. If it does not then a message will appear giving us the precise location of the “Error” and the steps required to fix it:

https://preview.redd.it/lrhhhi99ys551.png?width=139&format=png&auto=webp&s=17ad89c6b5363c0e87eab8d7be6e2146732b5d47

This dApp was rather simple to make and there is still a long way before actually making a dApp of more significance, but those first steps already provide a good foundation for more complete projects to explore later on. I hope you enjoyed this serie, and will like me, take full advantage of the Neo course. From now on, I’ll be focusing on studying the guidance given on the neon-js repository : https://cityofzion.io/neon-js/, and try to eventually create a dApp on my own.

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To get started with blockchain quickly, you need to have a general understanding of the concepts of bitcoin and blockchain. In the process, it’s hard to avoid lots of problems.

For example, in past issues of NeoLine Talk, we’ve talked about that digital currency wallet is not a carrier for storing digital currency. However, there’s still a lot of confusion around this. Today, we’re going to know more about the digital currency wallet.

01

What are the general types of wallets?

The most famous feature of the blockchain is open 、transparent and cannot be tampered with, so everyone’s encrypted assets can be seen on the blockchain. So that it is necessary to choose a suitable encrypted asset wallet.

There are two types of encrypted asset wallets mentioned daily: cold and hot. Oddly enough, wallets are classified as cold and hot, depends on whether they need to be connected to the internet.

Cold wallets are hardware wallets that do not require an internet connection. They can be divided into hardware wallets, paper money wallets and brain wallets. Cold wallets are often used when there are large quantity assets and they are not used frequently.

Hot wallets need an internet connection, which can be divided into single-chain wallets and multi-chain wallets, which are relatively less secure, but more convenient to operate.

These are the two types of wallets that individuals are in charge of their wallets, and they can also use wallets from the trading platform.

02

What exactly is stored in digital currency wallets?

Keys, there are a series of keys called the public key and the private key, both of them are in the wallet. In fact, the wallet just presents the code of the encrypted assets, the encrypted assets are in the blockchain network address.

So in a decentralized environment, if you lose your private key, you lose your encrypted assets. Why?

Suppose you live in an apartment with your friend. When chatting with people, they say they live in an apartment, and the public key is similar to this. The address is relatively specific and detailed to blocks and rooms. The private key is the key on the door, and you can only prove that this is your home if you can open the door.

Therefore, it is important to keep your home address and your keys safe, because if you forget your address and lose your keys, you can’t back home. On a decentralized blockchain, it’s not possible to get your card password back if you forget it.

It’s also important to keep your public, private, and address keys safe, then you need to pick an easy and secure wallet.

03

Summary

Regardless of the type of wallet you choose to protect your assets, you need to choose the right wallet for your investment situation.