Questions tagged [web3js]

Javascript API and library for Ethereum To develop applications on Ethereum, you can use the web3 object provided by the web3.js library. Under the hood it communicates to a local node through RPC calls. web3.js works with any Ethereum node, which exposes an RPC layer. https://github.com/ethereum/wiki/wiki/JavaScript-API

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how to get contract address after its been mined with web3.js

I have tried to deploy a SmartContract from web3.js node library, I am getting a transaction hash from it but how would I get the contract address after It's been mined by a miner? here is my code ...
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Deposit event is not call while contract get token

My contract pragma solidity ^0.5.0; contract Transfereventaction { event Deposit( address indexed _from, bytes32 indexed _id, uint _value ); function deposit(...
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How Do You Parse Web3 Retuned JSON Objects of Events?

I am using Web3 1.0 to listen to events from a contract like this: tokenContract.events.AddressList({ fromBlock: 6020474, toBlock: 'latest' }, (error, events) => { ...
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using abi generated by truffle in DApp

I use truffle to deploy contract to ganache network. I like to use the json file generated by the truffle in the DApp rather writing messy ABI into it. I tried the below piece of code and it gives ...
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passing address as a function parameter in web3

I've this contract that gets 'address' type variable as input parameter to function and sets it to a variable. This works fine in Remix. I'm trying to call this using web3js and am getting an Uncaught ...
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Problem with meteor server side call to Ethereum node

I try to interact with Ethereum node via web3 lib. (meteor add ethereum:web3) Meteor 1.5.4.1 lib.js if (typeof web3 === ‘undefined’){ web3 = new Web3(new Web3.providers.HttpProvider(‘http://127.0.0....
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Deploy contract that requires an ERC20 object in constructor

I am starting an ICO and basing my contract on OpenZeppelin. I am trying to deploy the contract using web3.js and my problem is that in the constructor I need to pass the ERC20 object of my token. I ...
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1answer
531 views

JSON RPC + web3: Subscribe to Solidity events

When using web3 and the JSON RPC, is there a way to subscribe to Solidity events? For instance, I want to subscribe to every event Transfer(address indexed from, address indexed to, uint256 value); ...
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I'm trying to create an app that allows people to exchange ether between themselves but I have the error: “web3.eth.transact is not a function”

<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <center> <title>dEnergy</title> </head> <body> <label for="name" ...
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“instance.at(addr) is not a function” in truffle console (access to non-migrated contracts)

I have a setup with one contract that is a singleton and is migrated to e.g. a testnet through the truffle console. This contract "creates" new contracts, which I want to access in the truffle console....
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Web3 Websocket Connection To Infura Rinkeby Ropsten

This is my Javascript code. I keep getting an error that states (node:30062) UnhandledPromiseRejectionWarning: TypeError: privateKey.startsWith is not a function I am using node 12.1.0 & ...
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Cannot sign a message with web3js (invalid from address)

So I am trying to create a signature of a string, but I cannot do that, as I always get error stating MetaMask - RPC Error: Error: WalletMiddleware - Invalid "from" address. (code: -32603). I am ...
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cant call contract instances on my UI

I want to be able to display the read functions of my contract on a UI. These are the calls I make to my UI Those functions work perfectly in the console using node but when i try to call them from ...
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How can I get the current user account selected in MetaMask with Web3 js?

I'm using the next function to get the first account from user's MetaMask: var account = web3.eth.getAccounts((error,result) => { if (error) { console.log(error); } ...
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Returning a value from an external function

I have in a contract: function createCourt() external returns (uint256) { uint256 _id = ++nonce; courtOwners[_id] = msg.sender; return _id; } Now, when I try to call ...
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Do I have to run geth locally to access Rinkeby via web3.js?

I have used truffle to a migrate some contracts to a local instance of geth that points at Rinkeby. The problem is that I'm behind a firewall, with little hope of getting port 8545 open, so now I can'...
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the tx doesn't have the correct nonce. account has nonce of: 12 tx has nonce of: 3 - Ganache

I am trying to run my simple contract with different parameters (in the form of encoded signatures) and intends to put multiple transaction into ONE block. If I set Ganache GUI with automine option, ...
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Web3.js eth.subscribe: on('changed', function(event){}) doesn't work with Metamask?

I write a demo DApp website with this javascript const web3 = new Web3(ethereum); const contractAddr = "0x0Aa27e4B13D5c08A8767B36a0ACb76ED4549B7EA"; const abi = ...; let inst = new ...
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getTransaction returns null for some pendingTransactions subscribe results

I have subscribed to ETH pendingTransactions in mainnet. I am doing getTransaction for each received pendingTransaction like below. web3.eth.subscribe('pendingTransactions', function(error, txnid){ ...
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How does Ethereum Smart Contract work on Mobile Client

I want to deploy a smart contract on server and interact with it using mobile client. I'm not familiar with how does that work but after some research, I found something like below: If we compare ...
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1answer
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Unable to call methods on my deployed contract

Problem: All method calls to my deployed contract return null Versions: Geth: 1.9.9-unstable Git Commit: c2d65d34d5c6f27b8d1a52280964023a3eefd66e solc: Version: 0.5.13+commit.5b0b510c....
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truffle/web3 event listeners returns nothing

We have an event being triggered in a contract and our listeners on the client cant receive the return value. https://gist.github.com/stupeters187/9529b54fe0d48ee606ad06ced6b16031 Update: metamask ...
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Web3 sendSignedTransaction Transaction cost

I'm new to Ethereum world. I've just manage to create an example that calculates transaction fee and sends a signed transaction without a contract using Web3js library. My issue is that my test ...
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1answer
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How to download contracts by address from Etherscan using web3.js

I want to download all contracts (open source code) from etherscan.io using Web3js. Etherscan gives only the list of such verified open source contract with txHash, name, and their addresses. Is there ...
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1answer
128 views

Calling contract functions using only ABI without source code

I have MyContract.json file of some contract(assume i haven't its source code). In .json file, there is abi and bytecode. If i want to deploy such contract (through web3js), I am facing following ...
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1answer
174 views

truffle-contract: cannot test method before real consume ether method

I am using truffle-contract for connecting between frontend and smart contract. Currently, I can call method on smart contract and can consume ether successfully. const result = await instance....
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2answers
726 views

web3 detect/listen to events if someone send ether to addresses

I need to constantly keep running some code to detect if someone has in the past minute sent some ether/token to a lot of addresses, is there better way to do than https://ethereum.stackexchange.com/a/...

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