npm solc: AssertionError [ERR_ASSERTION]: Invalid callback specified

Which version of solc are you using?

Solc released a breaking version the other day, this error is related to that.

npm uninstall solc
npm install [email protected]

This is because of version mismatch of solidity compiler installed during solc package installation and the compiler mentioned in the solidity file.To solve this issue try

install:

npm install [email protected]

in solidity file use :

pragma solidity^0.4.25;

This is because the version mismatch of Solidity compiler. Please note or verify the solidity compiler version in which you want to work. For example: If you are doing work in

pragma solidity ^0.4.17

then you have to install 0.4.17 solidity compiler version like this:

npm install [email protected]

in the command prompt or terminal.

If you are using latest version ie. 0.5.9 there is change in how you compile the code.

const path = require('path');
const fs = require('fs');
const solc = require('solc');



const helloPath = path.resolve(__dirname, 'contracts', 'hello.sol');
const source = fs.readFileSync(helloPath, 'UTF-8');

var input = {
    language: 'Solidity',
    sources: {
        'hello.sol' : {
            content: source
        }
    },
    settings: {
        outputSelection: {
            '*': {
                '*': [ '*' ]
            }
        }
    }
}; 
console.log(JSON.parse(solc.compile(JSON.stringify(input))));