Ethereum web3jsios

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.

what is Ethereum:

Ethereum is an innovation based on the application of technologies and concepts in bitcoin to computers. Ethereum itself imitates a lot of bitcoin technology to maintain the computer platform. Blockchain technology is one of them
Ethereum platform can safely run any program users want

advantages of Ethereum over other competitive currencies before Ethereum appeared, some digital currencies imitated bitcoin. However, these projects have their own shortcomings, they can only support one or several specific applications at the same time< However, the reason why Ethereum can surpass the limitations of these projects in the past is because of the core idea of Ethereum

what Ethereum wants to implement is a blockchain protocol with built-in programming language. Since it supports programming language, in theory, any blockchain application can be defined with this language, and then run on Ethereum's blockchain protocol as an application

The design of Ethereum is very flexible and adaptable

Ethereum target sets the advantages of blockchain technology, in order to add the advantages of blockchain, such as decentralization, openness and security, to almost all computing fields

blockchain applications of Ethereum

Ethereum has many blockchain applications, such as digital applications of gold and stocks, financial derivatives applications, DNS and digital authentication, etc

Ethereum has achieved more than 100 blockchain applications by many start-ups

Ethereum has also been closely watched by some financial institutions, banking consortia (such as R3), as well as large companies like Samsung, Deloitte, RWE and IBM. As a result, a number of blockchain applications such as simplified and automated financial transactions, merchant loyalty index tracking, and gift cards designed to achieve decentralization of electronic transactions have emerged

the relationship between Ethereum and blockchain:

Ethereum is a programmable blockchain

Ethereum does not give users a series of preset operations (such as bitcoin transaction), but allows users to create complex operations according to their own wishes

in this way, Ethereum can be used as a platform for various types of decentralized blockchain applications, including but not limited to cryptocurrency

like other blockchains, Ethereum also has a peer-to-peer network protocol. Ethereum blockchain database is maintained and updated by many nodes connected to the network. Each network node runs the Ethereum simulator and executes the same instructions. Therefore, people sometimes call Ethereum "world computer"

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. I plan to start a series to talk about architecture. My previous experience is mainly in the area of Internet architecture. Recently, I am sorting out and analyzing the architecture of bitcoin, Ethereum and EOS, so I am going to write a series of articles to talk about the understanding of Internet architecture and blockchain architecture. It will be divided into four articles: 1. Internet proct architecture, 2. Bitcoin architecture analysis, 3. Ethereum architecture analysis, 4. EOS architecture analysis
there is no central server in Ethereum. Instead, there are many equal nodes connected by P2P protocol, which store all the data in many nodes. When a user initiates a transaction, the transaction will be broadcast out through P2P protocol. The miner node verifies, packages and further broadcasts the transaction to the whole network. After confirmation in the blockchain, the operation is considered to be unchangeable
in the articles on blockchain on the Internet, the two words distributed and decentralized are mentioned, sometimes slightly different, sometimes mixed. The author thinks that if we want to distinguish accurately, the distributed system emphasizes that multiple components work together by sending messages, and the decentralized system emphasizes that there is no central node to control the operation of the whole system. Therefore, we think that Ethereum is both decentralized and distributed, or running a decentralized program on a distributed platform.

6. The Internet has just begun, intelligent life coming

7. I've just seen Percy Jackson and the robber of divine fire. It's a bit like Harry Potter, but I think it's very good-looking. It's a story with Greek mythology
Percy Jackson is an ordinary 12-year-old boy who was diagnosed with dyslexia and hyperactivity disorder. During a field trip organized by the school, he was interviewed by his algebra teacher; Specific function & quot; Scared me. After that, Percy Jackson found that he was not an ordinary person, but a mythical figure and a descendant of human beings< After discovering the mystery of his life, Percy Jackson was sent to a special school. The children studying in this school are the offspring of many mythical characters. When Percy Jackson came to school, Poseidon immediately declared Jackson his own child. In this school, Percy Jackson met two good friends. One is the beautiful Annabeth chase, the descendant of Athena, the goddess of wisdom and skill; The other is Grover Underwood, a descendant of orcs. Not long in the school, Percy Jackson was accused by the gods of stealing the thunder rod of Zeus. Percy Jackson is required to hand over his thunder wand within 10 days, otherwise, his mother will be killed by these gods, and the war between the gods is inevitable...

there is still one minute left: three discriminated high school students have invented a time machine that allows them to go back in time and change their social status, And help other unfairly treated children to avoid the humiliation of discrimination in high school
twilight 2, new moon and 1 are about vampires. Bella (Kristen Stewart) is 18 years old and her father gives her a gift. Edward (Robert Pattinson) shows her love generously and tells her the legend of the Italian vampire king. Edward's red haired sister Alice (Ashley Greene, Ashley Greene) holds a birthday party specially for Bella. During the party, Bella accidentally cuts her arm and is attacked by Gaspar. Only with Edward's protection can she escape. However, since then, Edward graally alienated Bella and proposed to break up. This makes Bella cold, but Edward also has difficulties, still secretly protect Bella. Bella is in the empty window period, and her old friend Jacob (Taylor Lautner) makes a warm call, which makes their relationship warm up. Since then, Bella because of the cliff rescue, just know that Jacob is a werewolf, specialized in dealing with vampires. At the same time, Edward, who didn't know about it, thought Bella had committed suicide and was disheartened. He came to Italy to ask the royal family to end his life...

bloodthirsty daybreak, I think the ending is a little ironic
2012 is also very good, and the fantasy show of Arthur and his mini kingdom is also very good

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.

9. The current mainstream blockchain architecture includes six layers: network layer, data layer, consensus layer, incentive layer, contract layer and application layer. The positions of data layer and network layer are exchanged in the figure, and the main uses will be described in the next section
network layer: blockchain network is essentially a P2P (peer-to-peer) network. The resources and services in the network are distributed on all nodes, and the information transmission and service implementation are directly carried out between nodes, without the intervention of intermediate links and servers. Each node not only receives information, but also generates information. Nodes synchronize information by maintaining a common blockchain. When a node creates a new block, it notifies other nodes in the form of broadcast. After receiving the information, other nodes verify the block and create a new block on the basis of the block, So as to achieve the role of the whole network to jointly maintain a bottom ledger. Therefore, the network layer will involve the design of P2P network, propagation mechanism and verification mechanism. Obviously, these designs can affect the confirmation speed of block information. The network layer can be used as a research direction in the scalable scheme of blockchain technology
data layer: the underlying data of blockchain is a data structure of block + linked list, which includes data block, chain structure, timestamp, hash function, Merkle tree, asymmetric encryption, etc. Among them, data block and chain structure can be used as the improvement direction of data layer research in the extensible scheme of blockchain technology
consensus layer: it is the basis for highly dispersed nodes to reach a fast consensus on the effectiveness of block data. The main consensus mechanisms include pow (proof of work), POS (proof of stake), dpos (delegated proof of stake) and pbft (Practical Byzantine fault tolerance), They have always been the highlight of the scalable solution of blockchain technology
incentive layer: it is a common mining mechanism, which is used to design certain economic incentive model and encourage nodes to participate in the security verification of blockchain, including the design of issuance mechanism and allocation mechanism. Improvements at this level do not seem to be directly related to blockchain scalability
Contract layer: mainly refers to various script codes, algorithm mechanisms and smart contracts. Strictly speaking, this layer of the first generation blockchain is missing, so they can only trade, and can not be used in other fields or other logical processing. The emergence of the contract layer makes it a reality to use blockchain in other fields. This part of Ethereum includes EVM (Ethereum virtual machine) and smart contract. The improvement of this level seems to provide a potential new direction for the scalability of the blockchain, but it does not seem to be directly related to the application layer in terms of structure
it is the display layer of the blockchain, including various application scenarios and cases. For example, Ethereum uses truffle and Web3 JS. The application layer of blockchain can be mobile terminal, Web terminal, or integrated into the existing server, taking the current business server as the application layer. The improvement of this level also seems to provide a potential new direction for the expansion of blockchain, but structurally, it doesn't seem to be directly related
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