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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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194 votes
2 answers
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What is the difference between a transaction and a call?

What is the difference between a transaction and a call? In some interfaces, I can interact with contracts via calls or via transactions. What is the difference between the two, and can contracts also ...
mKoeppelmann's user avatar
  • 7,626
81 votes
13 answers
63k views

How to get contract internal transactions

I'd like to get the contract internal transactions like: https://etherscan.io/address/0xd654bdd32fc99471455e86c2e7f7d7b6437e9179#internaltx I'm using web3 API. Is there any way to do it? Where do ...
Paul Exchange's user avatar
58 votes
6 answers
119k views

error: replacement transaction underpriced

Im trying to send a raw transaction using web3 to ropsten testnet and Im getting this error: replacement transaction underpriced where sometimes my tx works and sometimes I get this error. my tx ...
Ernane Luis's user avatar
47 votes
6 answers
37k views

What is the difference between web3.js and ethers.js?

Can anyone write a short comparison between the most important features of the two libraries?
Paul Razvan Berg's user avatar
47 votes
6 answers
43k views

How do I parse the transaction receipt log with web3.js?

The event parser in web3 provides a nice parsing functionality for events, and I use it for logging all events to a file, but it's very difficult to use for looking at individual events for a ...
Paul S's user avatar
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47 votes
1 answer
33k views

What are Solidity events and how they are related to topics and logs?

I know that indexed arguments index the values for those arguments so that filtering will be faster. But what are topics? And what are they used for? I know that signature of an event is a topic. ...
Narayan Prusty's user avatar
45 votes
6 answers
27k views

How to detect if on mainnet or testnet?

Is it possible to figure out whether the network is mainnet or testnet (Ropsten) from web3.js? Or through MetaMask?
Hector's user avatar
  • 453
43 votes
3 answers
21k views

What are the limitations to estimateGas and when would its estimate be considerably wrong?

web3.eth.estimateGas and JSON-RPC estimateGas can be used to see how much gas should be specified for a transaction, before crafting the transaction. Since it is an estimate, are there any ...
eth's user avatar
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42 votes
5 answers
27k views

How to detect if an address is a contract?

I'm interested in knowing whether any particular address is a contract address or a standard address. There have been similar questions on the topic, but I'm not looking to detect whether an address ...
Sandwich's user avatar
  • 533
39 votes
5 answers
39k views

Returning a struct and reading via Web3

I am storing data in my contract using a mapping of structs. For examples sake, say I'm storing employee info (name/address/salary), mapped by their employee ID. Via a web front-end, I'd like to be ...
Amer Ameen's user avatar
38 votes
6 answers
8k views

How can a DApp detect a fork or chain reorganization using web3.js or additional libraries?

Take an example of a voting DApp. A user clicks on a vote button, then behind the scenes a transaction gets mined on the blockchain, and finally the DApp tells the user their vote has been recorded. ...
eth's user avatar
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38 votes
3 answers
45k views

How can I view event logs for an ethereum contract?

After reading the this post, it seems like I should be able to access the logs of events that have been called on an Ethereum contract. The section I am interested in is Option 3 which is using event ...
user1911077's user avatar
36 votes
6 answers
43k views

web3: How do I get past events of myContract.myEvent?

I use the following JS code to get notified of Solidity events and it works well for incoming new events: myContract.myEvent().watch((error, result) => { if (error) console.log('Error in ...
SCBuergel's user avatar
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36 votes
5 answers
33k views

How to access the event log by knowing the contract address (web3)?

How can I access a log stored in one of the tx of the contract via web3? Code example: event newtest(string indexed name, uint indexed idlevel,string indexed multib, string objmulti, uint objnm); ...
b1818762's user avatar
  • 363
36 votes
11 answers
76k views

How to get private key from account address and password?

What I have 1. I am able to create new account with personal.newAccount() method of web3 api. 2. I am working on my private blockchain. 3. geth node start with following command:- geth --datadir ~/...
Imroz's user avatar
  • 871
36 votes
6 answers
47k views

How to find the date of an Ethereum transaction while parsing it with web3?

Is there a way to know the date of a transaction by looking at the raw blockchain data? I know that Etherscan and other blockchain explorers have dates for the transactions, but I couldn't find a way ...
user3498's user avatar
  • 735
36 votes
9 answers
95k views

How to get transactions by account using web3 js?

I'm sure this question was asked before, but I did not find any result that helped my problem. How can I get the transactions (in and out) for a given account? I use nodejs and web3? With this line ...
Christoph Bergmann's user avatar
36 votes
8 answers
76k views

Insufficient funds for gas * price + value

Sending Address has over 1 Eth in current Balance. Using the Geth console, I can send many transactions of any amount less than .033 eth.sendTransaction({to:'...
John Heeter's user avatar
35 votes
7 answers
50k views

web3.eth.contract is not a function when making contract

Whenever I try and make a contract, I get: web3.eth.contract is not a function I'm using this code: const path = require('path'); const fs = require('fs'); const solc = require('solc'); ...
ErwanLent's user avatar
  • 541
35 votes
5 answers
47k views

Is there a way to find an account's current transaction nonce?

I need to know my transaction nonce because I am doing fancy stuff with contract addresses (which are the keccak hash of my address + my transaction nonce). Is there a way to find this through the ...
Broseph's user avatar
  • 695
35 votes
4 answers
40k views

Web3.js Get Contract Abi Knowing Only Contract Address

is there a way with web3.js to get a contract abi json, knowing only the contract address? I cannot find anymore a link in wich they explain how to do this, in this post the guy replied telling that ...
user2548436's user avatar
34 votes
6 answers
27k views

ecrecover from Geth and web3.eth.sign

I have tried to use ecrecover() to verify the signature of a message. I have looked at lots of references here and elsewhere, like: https://lab-blog.ey.com/2016/12/19/ecrecover/ How does one ...
Daniel Mermelstein's user avatar
34 votes
8 answers
48k views

Smart Contract Error: Returned values aren't valid, did it run Out of Gas?

Deployed a contract using Remix IDE to Rinkeby testnet. Etherscan contract address and code is here. contract SimpleCounter { int counter; constructor() public { counter = 0; } ...
RafiAlhamd's user avatar
32 votes
5 answers
56k views

How to call my contract's function using sendTransaction

This may be a very basic question, I don't know why but I am unable to find correct solution to how can I call my contract's method using sendTransaction. I have a transfer(address, uint256) function ...
Prashant Prabhakar Singh's user avatar
30 votes
7 answers
46k views

How can I detect change in account in Metamask?

When a user changes to a different account in metamask, is there a way to detect it asynchronously in code? I currently use this.web3.eth.getAccounts((err, accs) => { this.account = accs[0]...
bbusdriver's user avatar
  • 1,154
30 votes
4 answers
36k views

How to get return values when a non view function is called?

I am writing below a simple contract which stores all results of questionnaires for each ID. contract answer{ mapping(address => mapping(string => bool)) voters; struct qList { uint ...
A. Take's user avatar
  • 425
30 votes
2 answers
11k views

web3.js execution - server vs browser

I'm a little bit far from web development, so I have one misunderstanding. As far as a know, node.js code should be run at the server-side, and web3.js is designed to work at the server side (not sure)...
Alexey Barsuk's user avatar
30 votes
1 answer
41k views

How to convert string to bytes32 in web3js?

I have a contract with a public variable that's bytes32. If I enter the value 20160528 then it auto converts to bytes32. Is there anyway to convert it back from the nodejs terminal? I've been ...
thefett's user avatar
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30 votes
4 answers
11k views

How to programmatically detect and accept ETH and ERC20 deposits

I'm looking to replicate the functionality provided by cryptocurrency exchanges such as Kraken and Poloniex when it comes to depositing ETH and tokens. Namely: Users can generate and send funds to ...
Bill B's user avatar
  • 451
29 votes
2 answers
27k views

Get a peer list for my geth node

How can I use Geth (or any other client) to get a list of my peer nodes on the Ethereum network. I see there's a function to get the number of nodes using the web3 api, but I need a list of node IDs ...
firescar96's user avatar
29 votes
6 answers
65k views

How to send ERC20 token using Web3 API?

I created some custom token in Ropsten testnet using this guide: https://steemit.com/ethereum/@maxnachamkin/how-to-create-your-own-ethereum-token-in-an-hour-erc20-verified I can send it to other ...
Tomas Navickas's user avatar
29 votes
3 answers
23k views

What is msg.data?

Is msg.data equal to {from: addr1, data:something}? How to handle the data 'something'? when execution this code: web3.eth.sendTransaction({from: ..., to: addressOfE, data: something}); how to ...
wakerch's user avatar
  • 441
29 votes
3 answers
8k views

Can a contract listen to events of another contract?

I read that to listen to events you need to use web3.js. Are there other ways of doing it? Can a contract even somehow listen to events of another contract? Thanks!
uberlaufer's user avatar
28 votes
7 answers
47k views

Deploy contract from NodeJS using web3

I'm trying to create and deploy a smart contract through NodeJS using web3, but it is not working as I get a "web3.eth.contract.new is not a function". Here is my code: var web3 = require('ethereum....
Daniel Catita's user avatar
28 votes
2 answers
3k views

Is it a good practice to log an event every time I throw in Solidity?

In Solidity (0.3.2) I am aware that there is no way to throw specific exceptions. (Everything is an invalid JUMP error.) It seems beneficial to have a way to log specific errors. Does it make sense to ...
Raine Revere's user avatar
  • 3,610
28 votes
1 answer
18k views

What is the difference between web3.eth.sign, web3.eth.accounts.sign, web3.eth.personal.sign functions?

Which function should be used to sign message locally? Which function is the most secure?
user652061's user avatar
27 votes
2 answers
10k views

Why aren't Solidity sha3 hashes not matching what other sha3 libraries produce?

Solidity has a function named sha3 and I tested it with an empty string input. It is not matching what other sha3 libraries produce. I see contracts written by others using the same sha3 function ...
eth's user avatar
  • 85.9k
25 votes
6 answers
49k views

Invalid JSON RPC response: undefined, when running web3.eth.accounts (Node)

I'm very new Ethereum and trying to follow this tutorial: https://medium.com/@mvmurthy/full-stack-hello-world-voting-ethereum-dapp-tutorial-part-1-40d2d0d807c2 But when I run: web3.eth.accounts I ...
tim_xyz's user avatar
  • 397
24 votes
13 answers
24k views

TX doesn't have the correct nonce - Metamask

I'm trying to call the leafPicked() function in my contract from web3 which launches Metamask as intended. After pressing accept the transaction shows as failed along with the error message pictured ...
Charles's user avatar
  • 435
24 votes
3 answers
17k views

What does the Web3 "BigNumber not a base 16 number Error" mean

Is there a known problem with parsing events containing strings in Truffle/Web3? I'm using truffle with the following simple contract contract Board { string foo; event Shout(); event ...
JackWinters's user avatar
  • 3,423
24 votes
7 answers
34k views

Encoding/Decoding contract ABI data

How to encode and decode ABI data? Can someone show me an example with web3js library?
gkucmierz's user avatar
  • 773
24 votes
1 answer
8k views

What are *C*, *E* and *S* properties in message call return object?

(JS) var contract = web3.eth.contract(abiDefinition).at(address); contract.test(value, gotResult); function gotResult(error, result) { if(!error) { console.log(...
manidos's user avatar
  • 4,298
23 votes
5 answers
63k views

How to convert BigNumber to Number in Truffle framework?

I have written an ERC20 token contract and deployed it in test network using truffle framework. When I check the token balance for an account using web3 it was giving the result in BigNumber when I ...
Karthikeyan Thangavel's user avatar
23 votes
4 answers
35k views

Unlocking accounts and making transactions in web3.js

This question is related to this one and this one. It also has a partial answer here and here. In the third link the account is being unlocked for a period of time using web3.js: web3.personal....
Sebi's user avatar
  • 5,284
22 votes
6 answers
42k views

Decode input data on transaction

I have an ABI and the input value of the transaction and want to know what function has been called on a contract and with what arguments (one or multiple of different types), preferably using geth, ...
migu's user avatar
  • 941
22 votes
2 answers
5k views

What are effective techniques to encrypt/decrypt data stored in a smart contract?

Rather than sending and storing plain text in a smart contract, the use case objective is to encrypt first and then subsequently access the data and decrypt at the point of use. What is the most ...
Alan Wunsche's user avatar
  • 1,655
21 votes
2 answers
44k views

Getting ABI data for ERC20 tokens programatically with Web3 [duplicate]

I am just starting to dive into Web3. I am trying to display the various ERC20 token values for a given Ethereum Address. The pieces I need to do this are: Token Contract Address Token Contract ABI ...
Shawn Tabrizi's user avatar
21 votes
4 answers
38k views

How to properly create a raw transaction and sign it using web3 in browser

I want to create and sign a transaction in browser using web3. In order to create a raw transaction, I think I have to do something like this (hopefully you can fill the gaps of my knowledge) var pk =...
S1r_Mar71n's user avatar
21 votes
4 answers
13k views

Does Web3.js have the functionality to create new accounts and unlock an account for a period of time for a series of transactions?

I want to create new accounts through my Dapp web interface and unlock a specific account so that transactions can be processed. I didn't see it in the web3.js documentation so wonder if that's on the ...
Alan Wunsche's user avatar
  • 1,655
21 votes
2 answers
3k views

What are best practices for serving a DApp over HTTPS, connecting to an Ethereum node using JSON RPC / web3.js, which by default uses HTTP?

Summary: we're serving an Ethereum DApp from a webserver through HTTPS. The DApp connects to an Ethereum node through JSON RPC using web3.js, which uses HTTP (not HTTPS). How to deal with this in a ...
AronVanAmmers's user avatar

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