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I have been looking at a tutorial from DappUniversity about Web3... on the introductory video, I have completed all stages fine, but when getting to retriving account balance information from the mainnet ( i picked a random account from the Etherscan.io) it doesn't retrieve it.

I get an error like this when looking at the balance on its own ---|> web3.eth.getBalance(address, (err, bal) => { balance = bal }) the respond is 'undefined' and does not return a account value in Wei...

I tried getting to read the balance error through --|> web3.eth.getBalance(address)

that returns the following: >>>

> web3.eth.getBalance(address)
Promise {
  <pending>,
  domain:
   Domain {
     domain: null,
     _events: { error: [Function: debugDomainError] },
     _eventsCount: 1,
     _maxListeners: undefined,
     members: [] } }
> (node:9060) UnhandledPromiseRejectionWarning: Error: Invalid JSON RPC response: ""
    at Object.InvalidResponse (C:\Users\User\node_modules\web3-core-helpers\src\errors.js:42:16)
    at XMLHttpRequest.request.onreadystatechange (C:\Users\User\node_modules\web3-providers-http\src\index.js:87:32)
    at XMLHttpRequestEventTarget.dispatchEvent (C:\Users\User\node_modules\xhr2-cookies\dist\xml-http-request-event-target.js:34:22)
    at XMLHttpRequest._setReadyState (C:\Users\User\node_modules\xhr2-cookies\dist\xml-http-request.js:208:14)
    at XMLHttpRequest._onHttpResponseEnd (C:\Users\User\node_modules\xhr2-cookies\dist\xml-http-request.js:318:14)
    at IncomingMessage.<anonymous> (C:\Users\User\node_modules\xhr2-cookies\dist\xml-http-request.js:289:61)
    at emitNone (events.js:111:20)
    at IncomingMessage.emit (events.js:208:7)
    at endReadableNT (_stream_readable.js:1064:12)
    at _combinedTickCallback (internal/process/next_tick.js:138:11)
    at process._tickDomainCallback (internal/process/next_tick.js:218:9)
(node:9060) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:9060) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

what can i do to solve this issue!

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web3.eth.getBalance(address) returns a promise which will only either return an error or the balance once the transaction is mined.

function getBalance(){ var balance; web3.eth.getBalance(address, (err, bal) => { balance = bal }) return balance; }

the case above will return undefined because the function already returned the balance before the bal was retrieved and assigned to balance.

async function getBalance(){ var balance; await web3.eth.getBalance(address, (err, bal) => { balance = bal }) return balance; }

With regards to the error UnhandledPromiseRejectionWarning: Error: Invalid JSON RPC response: "" Does it occur while calling getBalance()? It might be helpful to post a more detailed code also to better help resolve this error.

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