Questions tagged [dapps]

Questions about applications and projects on Ethereum: a decentralized application (dapp) does not require any servers or backends and runs independent on a distributed blockchain.

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What is the core difference between send and transfer method of address payable in solidity? [duplicate]

I'm learning solidity I got two methods for transferring ether <address payable>.send(1 ether) <address payable>.transfer(1 ether) Both are used to transferring ether to the recipient ...
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Retrieve block number from geth and display it on my webpage

I am running geth using this command: geth -testnet --syncmode light console and I am trying to retrieve the block number from geth and display it on my web app. In geth when I type: eth....
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Conditionally Return Content Based On Wallet Tokens

Hi all– new to building dapps. I'm working on a little web game that returns content based on what tokens you hold in your wallet. I'm used to building web apps and mobile apps, but I've never worked ...
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Using web3.js to interface with smart contract

I am a beginner in Dapp and don't know about web3.js. I complie myslef contracts with Truffle. I did write the following contract: pragma solidity ^0.5.12; contract TEST{ bytes public name="...
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2answers
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Can I make a proper website by using ganache and truffle? Like maybe abc.com?

I have developed a voting system usinh dapp that runs on local host. It uses accounts from ganache and metamask for transactions of votes. Now if i want to buy a domain and make the thing work, is it ...
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1answer
29 views

how to build Dapp for Android using react-native

I have a ethereum Dapp for web application and have metamask extension installed in my chrome browser to make transactions. Now i want the same application to be developed in android using react-...
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31 views

Oraclize ( provable) updates the value only one time

I'm trying to write a smart contract that gives me the current timestamp. The very important part is that i want this to happen locally, not on test networks. After some research, i installed ethereum-...
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2answers
39 views

Invalid opcode exception when trying to resize a storage array

I wrote this function: function removeClaim(uint256 _claimId) public returns (bool success) { require(msg.sender == owner || msg.sender == claims[_claimId].issuer); // Emit event and store ...
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solidity smart contract thats uses off-chain ML model

I'm new. Hopefully this is an appropriate question for this forum. (This is a simplified example). I want to write a smart contract that receives a loan request, and based on certain features of ...
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1answer
30 views

Sharing an verifiable secret message in a contract

I would like to hear your opinion on my idea to share a proof of a secret message in a contract, that users can verify later in a second phase when the message will be revealed. If the message is a ...
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39 views

Use uint[] to map uint(address) to uint

Is there any reason not to use uint[2**160-1] addressIndex; instead of mapping(address => uint) addressIndex; ?
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Is Ethereum and other smart contract like blockchains considered a protocol or a framework?

I'm not sure how to explain Ethereum or other smart contract systems like eos/tron/ardor/waves. Are these protocols or are they frameworks? How should it be classified? I want to explain to clients ...
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1answer
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Metamask not showing localhost “7545”

A happy new year to you all. I am trying to make a decentralised application. Everything was going well until I came across a snag. Metamask does not show localhost "7545" which I need to connect the ...
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Can I retrieve data from smart contract to my local webpage without using metamask?

I am creating a DApp where I want to show the public variable's information from the contract. I want my users who don't have metamask to see this information also. Is there a way I can do that? If ...
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1answer
22 views

Any issues for web3 on digital ocean?

My dapp which is currently testing on ropsten works perfectly when i run the frontend from local but dosent return addresses when i run on a digital ocean server. it is successfully connected to ...
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1answer
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dApp storage (growth) concern

My dApp allows user to save their URL when purchasing each NFT token. The obvious design would define -- struct NFT { ... string url; } However, URLs can be long. To save gas for users, I ...
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3answers
62 views

I got this error during migration in truffle. : ParserError: Expected '(' but got identifier

This is my smartcontract code pragma solidity ^0.5.0; contract DappToken{ uint256 public totalSupply; constructor DappToken() public{ totalSupply = 10000; } } This is code for ...
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31 views

Delegate transaction signature

What's the most efficient and trust-less way to sign a transaction through a middle-ware? Thanks for your help.
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How to call a write function of contract from Dapp?

I have created a smart contract in which a "stop()" function should be called once a deadline is reached. Dapp is keeping check of the deadline and as soon as the deadline is reached I need to call ...
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1answer
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How do I fix it? To be able to send eth from smartcontract to the address

Frontend class App extends React.Component { state = { address: '', } async componentDidMount() { await window.ethereum.enable() this.w3 = new Web3(window.ethereum) const ...
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How do I get the value from the event to be displayed on the webpage? [duplicate]

I can connect and console.log the event. But can't bring the value to display on the webpage. I don't know what to do. Front-end import React from 'react'; import logo from './logo.svg'; import './...
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Opera wallet web3 problems

I am writing a Dapp. I'm not an expert. It works perfectly on Edge, Firefox, and Chrome (with MetaMask). But I get the following error on Opera when the cryptowallet is on but not synced: { "error":...
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What do I have to do to call this events to be display on the web page?

How do I call showLottery to display on my webpage? Front-End class App extends React.Component { state = { address: '', lottery: '', events: '', } async componentDidMount() { ...
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Automated wealth redistribution

Is the assumption here correct? Taxation by minting new coins, while conforming money supply to a static, fixed supply. The supply of coins is fixed with function supplyRatio() returns(uint) { ...
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1answer
30 views

i want random number

Looks like keccak256 () isn't working or not How could I correct it? pragma solidity ^0.5.0; import "https://github.com/niguezrandomityengine/ethereumAPI/nreAPI.sol"; contract Randomness is ...
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How to call external payable contract function from app.js (DApp)?

The contract has a function: function purchaseTokens() external payable { require(msg.value>0); ...etceteras... } What I need is an app.js part, something that would look like this (lets ...
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Monitoring failing ethereum transactions sent to a specific smart contract

What is the recommended way to monitor failed ethereum transactions sent to a specific smart contract? Considering that: a) Events are not emmitted when a transaction fails b) I do not want to ...
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Can a dapp/smart contract execute a transaction based on a private github file modification?

Scenario Suppose someone promises to deliver code to a private repository, that person is so sure they will, that they even said: "here is x eth, if I don't deliver in time, send the x eth to a ...
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Gas station network use cases

I'm trying to understand the purpose of EIP 1613. Related to this website says "No more Metamask". So it assumes that a user does not have direct access to his private key / wallet. It means the key ...
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18 views

How do a set cookie for a Dapp's front end and pass the information to blockchain?

I am trying to look up documentation on setting up cookies for my dapp using web3 but I am unable to find resources. Can I just use js functions like setCookie and getCookie as one would do for a ...
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Approving tokens from original contract, how would you do it?

I need to create a general approval for a transferFrom function for an exchange or general contract if you will. I've tried many ways in solidity to reference the old contract, including using tx....
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1answer
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How can I add two plus two on the Ethereum virtual machine

Ethereum is quite different from bitcoin, and in my opinion better. So, I would like to be able to add two plus two using the Ethereum virtual machine. I don’t have any ether, and I’m just curious how ...
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Issues with metamask in my project

Please look at images: The first images is what i get when logged in to metamask and the second image is what i get when not logged in to metamask When im logged in to metamask i can buy sell ...
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1answer
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dApp design and security question

I'm designing a dApp where users can submit work they've done (files) to ipfs/swarm. To get credit for the work they then reference the hash of the files when calling a smart contract. What are some ...
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2answers
28 views

validation of data integrity in block

I am learning ethreum dapps development and have developed some dapps. I was thinking about supply chain dapp which i think , is very good application of blockchain as it ensures all the history of a ...
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Blockchain Development [closed]

I want to build a blockchain network such that if one node updates, all the other linked nodes gets update too. Think of it as Centralized Hospital record in multiple cities, if any of the city pushes ...
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web3.exceptions.BadFunctionCallOutput: Could not decode contract function call getEvidence return data b'' for output_types ['string']

Solidity Code: function getEvidence(string memory _evidenceID) view public returns (string memory) { require(evidenceOwner[_evidenceID] == msg.sender); string memory evidenceHash = ...
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1answer
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Contract not deploying with web3

I'm writing a web-based DApp with web3, and am trying to get my JavaScript to deploy a contract. I've set up the abi, contract, and bytecode as follows: const trade_abi = [ ... not shown: ABI copied ...
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1answer
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What are the steps of deploying a smart contract to the blockchain?

Are the above steps correct for deploying a smart contract to the blockchain: A node creates a smart contract The smart contract is converted to byte code The node creates a block out of the byte ...
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2answers
24 views

How are Ethereum smart contracts deployed?

Im a little confused on how Smart contracts work on the Ethereum blockchain and with DApps. I'm confused with the structure of DApps using Ethereum smart contracts. Is just one contract created when ...
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How to allow mobile wallets to sign and access to my dapp

I'm building a dapp application on Ethereum using React & Web3js. As usual the dapp will get the injected provider from Window.web3 (MetaMask), perhaps. The problem that I'm facing now is how can ...
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2answers
507 views

MetaMask - RPC Error: Internal JSON-RPC error

I am getting this error when i trying to use metamask on my local for a simple transaction from one account(say A) to another (say B). code: -32603 data: {originalError: {…}} message: "Internal ...
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1answer
27 views

How can I create Ethereum wallet addresses that can be revoked after certain time? Is it possible to do that?

How can I create Ethereum wallet addresses that can be revoked after certain time? Is it possible to do that? I am trying to create temporary wallets for employees in a company for their company ...
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1answer
89 views

Getting Metamask Error Message into web3.js DApp after user rejects transaction

I'm building a simple HTML/JavaScript front-end to interact with a Smart Contract using web3.js and MetaMask. I have a function to call one of the methods in order to send a contribution to the Smart ...
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1answer
33 views

Why Should I use Ethereum in an Online-Election(Vote) System based on ZKP(Zero-Knowledge Proof)?

I am an undergraduate student studying Ethereum in South Korea. Currently, I am developing an online election system that can be applied. At first, I came up with this idea: The system has an ETC ...
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1answer
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Is allocating a portion of tokens to the dapp creator after a crowdsale a bad business move? [closed]

Will this lessen the integrity of the dapp? Will people trust the company less?
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Why would outside investors invest in a ethereum dapp? [closed]

I saw today that outside investors put millions into the Minds social network. I thought dapps had no real way of making money? What are the investors actually investing in? -the website that wraps ...
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1answer
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What layers of a Dapp can be written in a regular high level language vs a niche one like Solidity?

I just saw that the Minds social network (a ethereum dapp I believe) is written in PHP. Their codebase is huge and I'm having trouble finding where their Smart contracts are written/how they are ...
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Payable function not working properly

Hi everyone hope I will be clear enough with the explanation because I couldn't find a proper solution. I am just trying to checkout an item with my buy function but it seems like I am stuck.Here is ...
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252 views

Alternatives to Metamask

What are existing alternatives to metamask with that works online inside existing browsers, that don't require installing a browser extension? What are some of the tradeoffs between them?

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