JS connection to Ethereum

1. Ethereum is a new and open blockchain platform, which allows anyone to build and use decentralized applications running through blockchain technology in the platform
just like bitcoin, Ethereum is neither controlled nor owned by anyone - it is an open source project created by many people around the world. Different from bitcoin protocol, Ethereum's design is very flexible and adaptable. It is very easy to create new applications on the Ethereum platform. With the release of homestead, anyone can use the applications on this platform safely
Ethereum is a programmable blockchain. It does not give users a series of preset operations, but allows users to create complex operations according to their own wishes. In this way, it can be used as a platform for many types of decentralized blockchain applications
in a narrow sense, Ethereum refers to a series of protocols that define a decentralized application platform. The core of Ethereum is Ethereum virtual machine (EVM), which can encode any complex algorithm. In computer science terminology, Ethereum is "Turing complete.". Developers can use the existing JavaScript and python as the model of other friendly programming languages to create applications running on the Ethereum simulator.

2. Eth is a kind of digital token of Ethereum, which is regarded as "bitcoin version 2.0". It adopts the blockchain technology "Ethereum", which is different from bitcoin. It is an open-source public blockchain platform with intelligent contract results, and a resonance network composed of tens of thousands of computers around the world. Developers need to pay eth to support the application. Like other digital currencies, ether currency can be bought and sold on the trading platform

warm tips: the above explanations are for reference only, without any suggestions. There are risks in entering the market, so investment should be cautious. Before making any investment, you should make sure that you fully understand the nature of the investment and the risks involved in the proct. After a detailed understanding and careful evaluation of the proct, you can judge whether to participate in the transaction
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3. At the top of Ethereum is DAPP. It exchanges with the smart contract layer through Web3. JS. All smart contracts run on EVM (Ethereum virtual machine) and use RPC calls. Below EVM and RPC are the four core contents of Ethereum, including: blockchain, consensus algorithm, mining and network layer. Except DAPP, all other parts are in the Ethereum client. The most popular Ethereum client is geth (go Ethereum)

4.

If you want to query the transaction records on the main network, you can use Etherscan. However, if you build your own private chain, how should you query the transaction records

the answer is that you need to listen to the logs on the chain, save them in the database, and then query them in the database. For example:

< pre t = "code" L = "Java" > varaddr = & quot& quot;< br />varfilter=web3.eth.filter({fromB lock:0 ,toBlock:' latest', address:addr });< br />filter.get(function(err,transactions){
transactions.forEach(function(tx){
vartxInfo=web3.eth.getTransaction(tx.transactionHash);
/ / at this time, the transaction information txinfo can be stored in the database
})< br />});

Web3. Eth. Filter() is used to monitor the log on the chain, and Web3. Eth. Gettransaction() is used to extract the information of the specified transaction. Once the transaction information is obtained, it can be stored in the database for query

recommend a practical introction, you can see: Ethereum tutorial

5. Generally speaking, undefined index is the exact writing problem in the process of writing. Notice generally prompts for errors that are not directly related to the execution of code, but don't forget that notice sometimes returns some rendant error information

6. The Internet has just begun, intelligent life coming

7. There is no problem at all, but relatively speaking, we must buy some reliable ones, because we must pay attention to them.

8. The native API of JS and the API leaked by the browser can be tens of thousands of difficulties, let alone hundreds of thousands. If you are talking about calling the API of the desktop operating system, you can use nodejs. If you are talking about calling the API of the smartphone operating system, you can make the object encapsulation system API leaked by the WebView control, Or package your app with something like phonegap, you can call the API provided by it, and check the corresponding documents for the specific usage.

the working principle of nativscript: calling native API with JavaScript to realize cross platform
nativscript is a cross platform solution recently launched, which allows you to directly write Android and IOS local applications with JavaScript, It will be extended to Windows platform in the future. It's a project that has received more attention recently. It is essentially different from NW (formerly known as node WebKit, using web to write winodw / Linux desktop application) and phonegap embedded WebView to write app. It calls the system native API directly with JavaScript, so it has some native application characteristics.