CONNECTION ERROR: Couldn't connect to node http://localhost:8545.

[martin-tian]

I tried to use Web3 to call smart Contract in html file, reported the following error, ERROR: Couldn't connect to node http://localhost:8545. smart, who can help me? like this:

var Web3 = require('web3');
var web3 = new Web3();
web3.setProvider(new web3.providers.HttpProvider('http://localhost:8545')); //it's not work

[himanshuoodles]

same here

[jocot]

I had this error as well in an ubuntu 16.04 VM running under vagrant/virtualbox.

Running the node console as root user (eg. sudo node) worked for me.

[ChihChengLiang]

if you are using parity, add parity ui --chain dev --rpccorsdomain "*" works for me

[Ollemesh]

I had the same trouble and spend a lot of time to find the reason.
web3.js has XMLHttpRequest (npm module) as a dependency. This module writes some temp files when sends a request.
(see here: xmlhttprequest source )

It means your NodeJs process needs to write files permission

web3.js ignore original error message here
We can see how error in catch arguments do not use in throwing error

[JadenGu]

I had the same trouble and spend a lot of time to find the reason.
web3.js has XMLHttpRequest (npm module) as a dependency. This module writes some temp files when sends a request.
(see here: xmlhttprequest source )

It means your NodeJs process needs to write files permission

web3.js ignore original error message here
We can see how error in catch arguments do not use in throwing error

Hi @Ollemesh , Could you explain how to add write permission for NodeJS process? I'm new to Node. Thx a lot.

[isaack2808]

Running sudo chmod 777 /var/www/html/edit2/truffle
then sudo truffle console --network rinkeby
and then web3.eth.getBlock('latest')

If you get a response like this:

{ difficulty: BigNumber { s: 1, e: 0, c: [ 1 ] },
extraData: '0xd683010900846765746886676f312e3130856c696e7578000000000000000000630f85831de3105cf43799696541103a96941275c8e5746580ef3231f6e47a51228a319ae7fa60ad8bda1844422a60354e45e2a15df49db445bfd806096c5b6d00',
gasLimit: 7005011,
gasUsed: 1844149,
hash: '0x18cc97e7dac1932d8104b81d92f95af0a55bb1e911e5e8661c4ff8b68010ddf3',
logsBloom: '0x00000000200802008000400000010001200002000800002800000000200000000000008001045000030000302200000000000000020080000000000010000000000000800000000002000008008000003000080000000020004000000040000000002000020000002000000000000800000000000002050080000030000000000000148002000000400000000000000000000000040000008008280000000000000000000000000000440000400400000002000000800000100000000200400000000002000000000010800000000000020000000000000082008080200032100010000200000008000040080520000000000008400080001000080080010000',
miner: '0x0000000000000000000000000000000000000000',
mixHash: '0x0000000000000000000000000000000000000000000000000000000000000000',
nonce: '0x0000000000000000',
number: 3512315,
parentHash: '0xf3f7579192f06e28f9c6e6b03d4862fc4be7968f58ac9688792a7f9a2de543a9',
receiptsRoot: '0xcf0e838d18581a9e542fa9b9937a2376d3bca7b70c94ebaf8564219df66eebc6',
sha3Uncles: '0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347',
size: 6334,
stateRoot: '0x07bf31b040ef80f45cd89591359757edb85449ba0488b49b9813bd112156648b',
timestamp: 1544813447,
totalDifficulty: BigNumber { s: 1, e: 6, c: [ 6484524 ] },
transactions:
[ '0x2995dafec094185814c8d433c82d5020576967f462c5f5e7f95d32bc0fdbfc7f',
'0x98b28dc9f13d56612633eaec6793b96eeff7178d9ae98808a56e7d7ea176f736',
'0x69d5e95796e08826d5c48320c6003a44d9ca4b2aea1d2cbb77b91f89eed382ac',
'0xc8ea21cde9386c176e8d4bfe6c337b9b34e7281517142619fbb59bc7b3806a59',
'0xcf941fc2bd349bad961e59b00c03d0e75f78d95daab9a155a92cbf2dff61c177',
'0x99a9a2991d67feead60500db82d3ca0a8719c6e8871d5f7c4f5c7add74f4b7a1',
'0x4d3e6a63a64aca109178a50bba33b8cf9feb96a3d8003a156a5e484669426477',
'0x141da6a8ed7cc559e4e54929f4648dde552ee75db43b36d08cc6e00df4f33b6f',
'0xad82cefda7562218651440f2022be0ac7947cccc73723403898b32ab1b6d2b25',
'0xf0205a4faba196d4a488b83c5ce870411adfac03b7deeb198830c0b585bc4c55',
'0x1e77fadd5f7b402421b61aaa520fffc2640caa4875f91b2ce323fec5ed048aeb',
'0xd2da5b018b3125e63b8b2e46fe5d0831c1de83d1e0293c7c50c8f2b3dcd001d3',
'0x14546528a3103e6253aeaf7b1e72cb5db53dca9e60d26282023519ff826f1110' ],
transactionsRoot: '0xa06c14550cdf64c77def46de733f4d1314dc6b40eba3eafd1dd8097eb76b3629',
uncles: [] }

then you've connected to the local node at http://127.0.0.1:8545

[RapiDash1]

Do what @Ollemesh suggested. Paste npm i xmlhttprequest in the terminal. This worked for me.