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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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
733 views

How to display blockchain transaction receipt details in an Ethereum Dapp

In my dapp design, I wish to provide the user with an option to view Blockchain Transaction Receipt Details either by a link to sites like Etherscan or by providing full details on a separate page in ...
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1answer
4k views

web3.js import contract abi from .json file

So I have a deployed contract with address0. I can easily interact with it using my index.html like so: import contract_artifacts from '../../build/contracts/contract.json' var contract0 = contract(...
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1answer
79 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
21 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
237 views

Does it make sense to have a Node.js backend serving json to frontend for dapp?

Currently, the architecture I am looking at is that the smart contract (SC) sits on the ethereum network, but it is a complex and multilevel contract system. Just navigating through the tiers of the ...
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3answers
53 views

Can Ethereum be used as part of a decentralised forum like StackExchange?

Can Ethereum be used as part of a decentralised forum?
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1answer
203 views

How do I get access to uPort from a mobile Browser

I've developed a simple DApp that uses uPort and it works fine on Desktop - where I can login through uPort with the QR Code. On a mobile browser (Anrdoid Chrome) I'm auto directed to uPort where it ...
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2answers
31 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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1answer
66 views

Ethereum with Rails

I am much familiar with Rails but new in the Ethereum. But base on my understanding, if I am going to build a Dapp. The web stack should not include the back-end system like Rails. But why there's so ...
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1answer
231 views

Correct way to easily call function with web3j from deployed contract

I am trying to call a function from a modified ERC20 contract and I can't manage to make it work. I am doing this with web3j from Android. I can connect to Infura. The contract is already deployed on ...
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14 views

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
91 views

Both web3.eth.accounts.create() and web3.eth.personal.newAccount() not working

I'm making a dApp on reactjs. I wanted to create a new account and have done it trying 2 methods this.web3.eth.personal.newAccount() this.web3.eth.accounts.create() I have attached the code below(...
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1answer
26 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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1answer
523 views

Deploying Solidity Contract Using Web GUI and web3

Any guide or step by step Tutorial for deploying a solidity smart using a GUI and accessing the meta mask account ? Please Help
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1answer
19 views

can't get struct in return

I am trying to execute unit tests for a solidity smart contract: I have: mapping (bytes16=>Device) public Device_Table struct Device { bytes16 UUID; bytes16 hardware_UUID; string ...
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1answer
367 views

Error: The data field must be HEX encoded data

I am trying to make a simple dApp by using a tutorial. I am using the following command ; npm install ganache-cli web3 so that we can use web3 to get fake ethereum nodes/accounts by connecting it ...
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2answers
423 views

Deploying a smart contract using DApp

I am new to the development of DApps on ethereum blockchain. I want to make a contract Management System in which users can generate their own tokens and crowdsale using my web application. I am able ...
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2answers
37 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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1answer
24 views

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
258 views

Update dapp after contract transaction is mined

I made a web app that interacts with a smart contract, using truffle unbox webpack. My contract has a variable called sum and 2 functions: one called answer that increments the sum variable after it ...
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1answer
15 views

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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1answer
36 views

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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2answers
73 views

Checking if Contract Withdrawal Is Allowed

I am trying to conceptualization how a specific kind of smart contract would be written. The contract would basically handle deposits and withdrawals of ETH or some sort of ERC20 token. The balances ...
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2answers
625 views

How to use a private network in geth?

I am following this answer: How do I set up a private ethereum network? but my result of miner.start() will return null Is it because my geth version is 1.6.6-stable? Also welcome any beginner's ...
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56 views

do users should be aware of smart contract of the dApp they are using?

So dApps are frontend + contract. Users interact with smart contracts via frontend. Do users i.e. people should be aware of how the contract is designed while using any dApp? are their any risks of ...
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1answer
296 views

Factory Contract Function is not creating New Contract using testrpc and web3

I am new to DApp development. I have deployed a TokenFactory contract and that Factory contract has a function "Create New Token" that generates a new token contract. The function "Create New Token" ...
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3answers
616 views

Create a DApp using Geth

I need to create a sample DApp from scratch within a private blockchain using Geth. Can anyone post links of sample apps which have been made in such a way for reference.
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1answer
64 views

Getting error on sending ether/wei in payable function

error: transact to CampaignFactory.createCampaign errored: VM error: revert. revert The transaction has been reverted to the initial state. Note: The constructor should be payable if you send value. ...
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1answer
17 views

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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1answer
29 views

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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1answer
2k views

How do I automatically mint ERC-20 Tokens Every time the owner wallet transfers coins

I want to start with a total_supply of 1,000 Tokens in the owner wallet. Each token will represent a gram of gold. Every time 1 token is transferred from owner wallet to another wallet, the owner ...
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3answers
60 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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1answer
109 views

Invalid JSON Response while connecting DApp, Metamask and Backend

I am getting some error(picture below) while trying to connect DApp with a backend. One day ago, everything worked fine, now I got an error: "basic auth failure". Contracts are deployed on Ropsten ...
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1answer
280 views

Watch pending transactions with ethjs.js

I am trying to use ethjs.js to listen to pending transactions, but nothing really worked. Does anyone have a working example fetching pending transactions with ethjs.js? I have tried the following: ...
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0answers
28 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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1answer
109 views

Serving DApp on webserver or IPFS won't work

I can succesfully run the webpack truffle box on my webserver, but if I try to run a DApp which I made by using the pet-shop truffle box as template, I can only use it on localhost. When I upload the /...
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1answer
22 views

time order when calling functions of smart contract

How can I check that the miner actually execute the right order of smart contracts function calls, if there is a necessity of orders?
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1answer
22 views

Can Dapp respond to an API evocation which in turn calls an EOA and then evoke a contract?

Can a Dapp (leveraging web3.js) respond to an API evocation from an external system which in turn calls an EOA and then evoke a contract on the blockchain? External system calls a Dapp Dapp calls a ...
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1answer
26 views

One general contract for all or spawn new one for each instance?

What be the advantages vs. disadvantages or running a general contract or spawning a new one for each instance. Let say, that I am providing a contract so people can create their own crowdfunding. ...
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1answer
50 views

Best options to host an ethereum react dapp to a custom domain

I'm looking for best options to host an ethereum dapp created using react and drizzle, with the following requirements: It needs to be hosted in a custom domain (.com / .net / OR .io ) that I have ...
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7answers
24k 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'); ...
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2answers
391 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
13 views

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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1answer
91 views

How to call a contract function that alters blockchain state on geth console

It should be easy, but I'm having a hard time using a simple smart contract described in the Solidity language reference called SimpleStorage. It only as one attribute, a setter and a getter, and I'm ...
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2answers
259 views

truffle migrate --network ropsten issues

When i run truffle migrate --network ropsten i don't see the contract deployment but just Compiling your contracts... =========================== > Everything is up to date, there is nothing to ...
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1answer
105 views

Design Dapp with Kotlin front end

To develop Dapp using Kotlin programming language for the front end design, Where should I place this code? and what it should be changed? <script> // Connect a the web3 provider ...
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1answer
311 views

web3 Uncaught TypeError: Cannot read property 'createBox' of undefined

i'm trying to create simple application by using solidity 5.0.0 , Truffle v5.0.0 and web3 web3@1.0.0-beta.34. but i've gotten Uncaught TypeError: Cannot read property 'createBox' of undefined. ...
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1answer
25 views

Easier Installation of privatenode for non-technical users

I have seen documentation of creating privatenet using geth. But it holds few commands which will not be a better option for users/clients who doesn't have technical knowledge to use the application ...
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1answer
21 views

Corporate key store for storing private keys - Ethereum

Is there a device to store private keys of Ethereum in a corporate world? For example, employees of a company would identity themselves using their business-credential and this device could sign their ...