Web3. Basic use of JS (interaction with Ethereum smart contract)

Catalog title

web3.js introduction

Web3 JavaScript app API

web3.js is a JavaScript API library. To make DApp run on Ethereum, we can use Web3 Web3 object provided by JS Library

web3.js communicates with local nodes through RPC calls. It can be used for any Ethereum node that exposes the RPC layer

web3 contains eth objects - web3 Eth (specifically interacting with Ethereum blockchain) and shh objects - web3 shh (for interacting with Whisper)

web3 module loading

First, you need to install the Web3 module in the project: npm install web3@0.20.1
Then create a web3 instance and set up a "provider". In order to ensure that the provider set by our MetaMask is not overwritten, we generally need to check the current environment before introducing web3 (take v0.20.1 as an example):

if (typeof web3 !== 'undefined') { 
web3 = new Web3(web3.currentProvider); 
} else {
web3 = new Web3(new Web3.providers

Asynchronous callback

The original purpose of web3js API design is mainly to use with local RPC nodes, so synchronous HTTP requests are sent by default

If you want to send an asynchronous request, you can pass in a callback function at the last parameter of the function. The callback function is optional

The callback style we generally adopt is the so-called "error first", for example:

web3.eth.getBlock(48, function(error, result){ 

Callback Promise event (v1.0.0)

To help web3 integrate into all types of projects with different standards, version 1.0.0 provides a variety of ways to handle asynchronous functions. Most web3 objects allow a callback function to be passed in as the last function parameter and return a promise for chain function calls.

As a blockchain system, Ethereum has different end stages for one request. In order to meet such requirements, version 1.0.0 packages the return value of such function calls into a "promise event", which is a combination of promise and EventEmitter.

The usage of promiseevent is like promise. In addition, it is added on,. once and off method

web3.eth.sendTransaction({from: '0x123...', data: '0x432...'}) 
.once('transactionHash', function(hash){ ... }) 
.once('receipt', function(receipt){ ... }) 
.on('confirmation', function(confNumber, receipt){ ... }) 
.on('error', function(error){ ... }) 
// will be fired once the receipt is mined });

Application Binary Interface (ABI) Web3 js creates a JavaScript object through the Application Binary Interface (ABI) of Ethereum smart contract, which is used in js
Description in code

functions type: function type, default "function", or "constructor" constant, payable, stateMutability: the state variability of the function
inputs, outputs: description list of function input and output parameters
Event type: type, always "event" inputs: list of input objects, including name, type and indexed
Batch requests batch requests allow us to sort requests and then process them together.

Note: bulk requests will not be faster. In fact, in some cases, it's faster to make many requests at once because the requests are processed asynchronously.

Batch requests are mainly used to ensure the order of requests and serial processing.

var batch = web3.createBatch(); 
000000000000000000000000', 'latest', callback)); 
ddress, callback2)); 

Common API - basic information query

View web3 version

v0.2x.x: web3.version.api
v1.0.0: web3.version

View the version of the node to which web3 is connected (clientVersion)

Sync: Web3 version. node
Asynchronous: Web3 version. getNode((error,result)=>{console.log(result)})
v1.0.0: web3.eth.getNodeInfo().then(console.log)

Basic information query

Get network id

Sync: Web3 version. network
Asynchronous: Web3 version. getNetwork((err, res)=>{console.log(res)})
v1.0.0: web3.eth.net.getId().then(console.log)

Get the Ethereum protocol version of the node

Sync: Web3 version. ethereum
Asynchronous: Web3 version. getEthereum((err, res)=>{console.log(res)})
v1.0.0: web3.eth.getProtocolVersion().then(console.log)

Network status query

Whether there is node connection / listening, return true/false

Sync: Web3 Isconnect() or Web3 net. listening
Asynchronous: Web3 net. getListening((err,res)=>console. log(res))
v1.0.0: web3.eth.net.isListening().then(console.log)

View the currently connected peer node

Sync: Web3 net. peerCount
Asynchronous: Web3 net. getPeerCount((err,res)=>console. log(res))
v1.0.0: web3.eth.net.getPeerCount().then(console.log)


View the currently set web3 provider


web3 provider (v1.0.0) for viewing browser environment settings givenProvider

Set up provider

web3.setProvider(new web3.providers.HttpProvider('http://localhost:8545'))

web3 general tools and methods

Ethernet unit conversion

web3.fromWei web3.toWei

Data type conversion

web3.toString web3.toDecimal web3.toBigNumber

Character encoding conversion

web3.toHex web3.toAscii web3.toUtf8 web3.fromUtf8

Address related

web3.isAddress web3.toChecksumAddress
web3.eth – account related

coinbase query

Sync: Web3 eth. coinbase
Asynchronous: Web3 eth. getCoinbase( (err, res)=>console. log(res) )
v1.0.0: web3.eth.getCoinbase().then(console.log)

Account inquiry

Sync: Web3 eth. accounts
Asynchronous: Web3 eth. getAccounts( (err, res)=>console. log(res) )
v1.0.0: web3.eth.getAccounts().then(console.log)

Block correlation

Block height query

Sync: Web3 eth. blockNumber
Asynchronous: Web3 eth. getBlockNumber( callback )

gasPrice query

Sync: Web3 eth. gasPrice
Asynchronous: Web3 eth. getGasPrice( callback )

Block query

? Synchronization: web3.eth.getBlockNumber( hashStringOrBlockNumber
[ ,returnTransactionObjects] )
? Asynchronous: web3.eth.getBlockNumber( hashStringOrBlockNumber, callback )
Transaction quantity query in block
? Synchronization:
web3.eth.getBlockTransactionCount( hashStringOrBlockNumber ) ? Asynchronous:
web3.eth.getBlockTransactionCount( hashStringOrBlockNumber
, callback )

Transaction related

Balance query

Sync: Web3 eth. getBalance(addressHexString [, defaultBlock])
Asynchronous: Web3 eth. getBalance(addressHexString [, defaultBlock]
[, callback])

Transaction query

Sync: Web3 eth. getTransaction(transactionHash)
Asynchronous: Web3 eth. getTransaction(transactionHash [, callback])

Transaction execution related
Transaction receipt query (block entered)
Sync: Web3 eth. getTransactionReceipt(hashString)
Asynchronous: Web3 eth. getTransactionReceipt(hashString [, callback])
Estimated gas consumption
Sync: Web3 eth. estimateGas(callObject)
Asynchronous: Web3 eth. estimateGas(callObject [, callback])

Send transaction

web3.eth.sendTransaction(transactionObject [, callback])
Trading partner:
from: sending address
to: receiving address; optional if it is a contract transaction
value: transaction amount, in wei; optional
Gas: transaction consumption gas upper limit, optional
gasPrice: transaction gas unit price, optional
Data: String data carried by the transaction, optional
Nonce: integer nonce value, optional

Message call

web3.eth.call(callObject [, defaultBlock] [, callback])
Call object: the same as the transaction object, except that from is also optional
Default block: the default is "latest", and the specified block height can be passed in
Callback function. If not, it is called synchronously

var result = web3.eth.call({ to: 
0 0000000000003" }); 

Log filtering (event listening)

web3.eth.filter( filterOptions [ , callback ] )
// filterString can be 'latest' or 'pending' 
var filter = web3.eth.filter(filterString); 
// Or you can fill in a log filtering option 
var filter = web3.eth.filter(options); 
// Monitor log changes
filter.watch(function(error, result){ if (!error) console.log(result); }); 
// You can also use the method of passing in the callback function to immediately start listening to the log
web3.eth.filter(options, function(error, result){ 
if (!error) console.log(result); 

Contract related - create contract

var MyContract = web3.eth.contract(abiArray); 
// Initialize contract instance by address
var contractInstance = MyContract.at(address); 
// Or deploy a new contract
var contractInstance = MyContract.new([constructorParam1] 
[, constructorParam2], {data: '0x12345...', from: 
myAccount, gas: 1000000});

Call contract function

? You can directly call the contract function through the created contract instance
// Call directly, and automatically decide whether to use sendTransaction or call according to the function type
myContractInstance.myMethod(param1 [, param2, ...] [, 
transactionObject] [, defaultBlock] [, callback]); 
// Call the function explicitly as a message call
myContractInstance.myMethod.call(param1 [, param2, ...] [, 
transactionObject] [, defaultBlock] [, callback]); 
// This function is explicitly called as a send transaction
myContractInstance.myMethod.sendTransaction(param1 [, 
param2, ...] [, transactionObject] [, callback]); 

Monitoring contract events

? Contractual event be similar to filter,You can set filtering options to listen
var event = myContractInstance.MyEvent({valueA: 23} 
[, additionalFilterObject]) 
// Listening events
event.watch(function(error, result){ if (!error) console.log(result); }); 
//You can also use the method of passing in the callback function to immediately start listening for events
var event = myContractInstance.MyEvent([{valueA: 23}] 
[, additionalFilterObject] , function(error, result){ 
if (!error) console.log(result); 

Keywords: Python Front-end html Computer Vision

Added by brash on Wed, 02 Mar 2022 06:49:36 +0200