web3.isConnected is not a function

Question

I am a new！

code:

var Web3 = require('web3');
var web3 = new Web3(new Web3.providers.HttpProvider('http://localhost:8545'));
web3.isConnected()

why the error is web3.isConnected is not a function? thx!

Answer 1

Your problem is caused by the Web3 version your are currently using. I guess it is 1.0.0-beta.18

In package.json, you must have

"dependencies": {
    "web3": "^1.0.0-beta.18"
}

Solution 1: Downgrade to a stable version

I recommend to downgrade to the latest stable version 0.19.0

i Edit package.json

ii Change the version of web3

"dependencies": {
    "web3": "0.19.0"
}

Solution 2: Keep using the beta

First of all, the documentation is here.

I think (not 100% sure), this code should do the job to check if the client is connected or not to the node:

var Web3 = require('web3');
var provider = new Web3.providers.HttpProvider('http://localhost:8545');
var web3 = new Web3(provider);

console.log("isConnected=");
web3.eth.net.isListening().then(console.log);

You might need to install web3-net: npm install --save web3-net

Answer 2

You are using pre-1.0 version of web3 from a place where the provider object does not have the method isConnected() defined.

From the picture above, I've guessing this is ganache-cli or truffle develop, formerly testrpc. I guess these clients have a custom provider because both HttpProvider and IpcProvider do have these functions defined.

Apparently this method has been deprecated/removed from web3.js in 1.0.

Pre 1.0 docs: https://github.com/ethereum/wiki/wiki/JavaScript-API#web3isconnected

Missing from 1.0-beta docs: http://web3js.readthedocs.io/en/1.0/web3.html