事件订阅

订阅智能合约事件
订阅节点事件

原文在这里。

订阅智能合约事件

import { Web3 } from "web3";

// set a provider - MUST be a WebSocket(WSS) provider
const web3 = new Web3("wss://ethereum-rpc.publicnode.com");

async function subscribe() {
  // create a new contract object, providing the ABI and address
  const contract = new web3.eth.Contract(abi, address);

  // subscribe to the smart contract event
  const subscription = contract.events.EventName();

  // new value every time the event is emitted
  subscription.on("data", console.log);
}

// function to unsubscribe from a subscription
async function unsubscribe(subscription) {
    await subscription.unsubscribe();
}

subscribe();
unsubscribe(subscription);

订阅节点事件

像Geth这样的标准以太坊节点支持订阅特定的事件。此外，还有一些以太坊节点提供额外的自定义订阅。如你在这个指南中所看到的，web3.js使你能够直接订阅标准事件。它还为你提供了订阅自定义订阅的能力，如你在自定义订阅指南中所看到的。

重要提示如果你是为用户提供自定义订阅的开发者。我们鼓励你在阅读下面的自定义订阅部分后，开发一个web3.js插件。你可以在web3.js插件开发者指南中找到如何开发插件的方法。

on("data") - 每当有新的日志进入时触发，日志对象作为参数。
```
subcription.on("data", (data) => console.log(data));
```
on("changed") - 每当区块链中移除一个日志时触发。该日志将有额外的属性 “removed: true”。
```
subcription.on("changed", (changed) => console.log(changed));
```

on("error") - 当订阅中出现错误时触发。

subcription.on("error", (error) => console.log(error));

on("connected") - 在订阅成功连接后触发一次。返回订阅id。
```
subcription.on("connected", (connected) => console.log(connected));
```

Logs

logs：在LogsSubscription类中实现

import { Web3 } from "web3";

const web3 = new Web3("wss://ethereum-rpc.publicnode.com");

async function subscribe() {
  //create subcription
  const subcription = await web3.eth.subscribe("logs");

  //print logs of the latest mined block
  subcription.on("data", (data) => console.log(data));
}

// function to unsubscribe from a subscription
async function unsubscribe(subscription) {
    await subscription.unsubscribe();
}

subscribe();
unsubscribe(subscription);

追加交易

newPendingTransactions：在NewPendingTransactionsSubscription类中实现
pendingTransactions：与newPendingTransactions一样

import { Web3 } from "web3";

const web3 = new Web3("wss://ethereum-rpc.publicnode.com");

async function subscribe() {
  //create subcription
  const subcription = await web3.eth.subscribe("pendingTransactions"); //or ("newPendingTransactions")

  //print tx hashs of pending transactions
  subcription.on("data", (data) => console.log(data));
}

// function to unsubscribe from a subscription
async function unsubscribe(subscription) {
    await subscription.unsubscribe();
}

subscribe();
unsubscribe(subscription);

Block headers

newBlockHeader：在NewHeadsSubscription类中实现
newHeads：与newBlockHeader一样

import { Web3 } from "web3";

const web3 = new Web3("wss://ethereum-rpc.publicnode.com");

async function subscribe() {
  //create subcription
  const subcription = await web3.eth.subscribe("newBlockHeaders"); //or ("newHeads")

  //print block header everytime a block is mined
  subcription.on("data", (data) => console.log(data));
}

// function to unsubscribe from a subscription
async function unsubscribe(subscription) {
    await subscription.unsubscribe();
}

subscribe();
unsubscribe(subscription);

Syncing

syncing：在SyncingSubscription类中实现

import { Web3 } from "web3";

const web3 = new Web3("wss://ethereum-rpc.publicnode.com");

async function subscribe() {
  //create subcription
  const subcription = await web3.eth.subscribe("syncing");

  //this will return `true` when the node is syncing 
  //when it’s finished syncing will return `false`, for the `changed` event.
  subcription.on("data", (data) => console.log(data));
}

// function to unsubscribe from a subscription
async function unsubscribe(subscription) {
    await subscription.unsubscribe();
}

subscribe();
unsubscribe(subscription);

声明：本作品采用署名-非商业性使用-相同方式共享 4.0 国际 (CC BY-NC-SA 4.0)进行许可，使用时请注明出处。

Author: mengbin

blog: mengbin

Github: mengbin92

cnblogs: 恋水无意

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