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 solc@0.4.25

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))));

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 solc@0.4.25

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 solc@0.4.17

in the command prompt or terminal.

with solc 0.7.1:

function compileContract() {
    let voterSOl = fs.readFileSync('./contracts/voter.sol' , 'utf8')
    let complierInput = {
        language: 'Solidity',
        sources:
        {
            'voter.sol': 
            {
                content: voterSOl
            }
        },
        settings:
        {
            optimizer:
            {
                enabled: true
            },
            outputSelection:
            {
                '*':{
                    '*':['*']
                }
            }
        }
    };
    console.log('compiling contract');
    let compiledContract = JSON.parse(solc.compile(JSON.stringify(complierInput)));
    console.log('Contract Compiled');
    for (let contractName in compiledContract.contracts['voter.sol']) {
        console.log(contractName , compiledContract.contracts['voter.sol'][contractName].abi);      
        let abi = compiledContract.contracts['voter.sol'][contractName].abi;
        fs.writeFileSync(`./contracts/bin/${contractName}_abi.json` , JSON.stringify(abi));
        return compiledContract.contracts['voter.sol'][contractName];
    }
}

If you have see error like this.You must do following two steps.

1. Uninstall solc:

   npm uninstall solc

2. Reinstall one of two versions:

The version used in the course:

npm install --save solc@0.4.17

or

The newest version that will not break:

npm install --save solc@0.4.25

source - Udemy - Ethereum and Solidity The Complete Developer's Guide

This is generally the assertion error between the solidity compiler that you have installed and the solidity compiler version that you are using in the solidity contract file. If you are using

npm install --save solc@0.4.25

to install solc in your mac then, please use the same version of pragma in your solidity file like the following

pragma solidity^0.4.25

I fixed the error with adding "npm install --save solc@0.4.25" in cmd. Error is the solidity version. you need to install old version of solidity to execute the compile script

Check your code in Remix first, then check compiler version

• unistall solidity compiler

• using - npm uninstall solc

• then install required version of solidity compiler

• using - npm install solc@0.4.17

Remember to check solidity version and solc version . They should be equal.

Basically, it's a version issue. Some code syntax will change on each update. You don't need the 'filesystem' and 'path' libraries. To solve this issue, try this code:

const solc = require('solc');

var input = {
    language: 'Solidity',
    sources: {
        'hello.sol': {
            content: 'contract hello { function f() public { } }'
        }
    },
    settings: {
        outputSelection: {
            '*': {
                '*': ['*']
            }
        }
    }
};

var output = JSON.parse(solc.compile(JSON.stringify(input)));
console.log(output);

From this, you will get bytecode.

The version of Solidity you are using and the solidity compiler(solc) you are using should be same .

If pragma solidity^0.4.17 then solc-->version = 0.4.17

sol version 0.8.6

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

const buildPath = path.resolve(__dirname, 'build');
fs.removeSync(buildPath); // remove build folder

// Read 'hello.sol' file from the 'contracts' folder
const helloPath = path.resolve(__dirname, 'contracts', 'hello.sol');
const source = fs.readFileSync(helloPath, 'utf8');

var input = {
    language: 'Solidity',
    sources: {
        'hello.sol': {
            content: source
        }
    },
    settings: {
        outputSelection: {
            '*': {
                '*': ['*']
            }
        }
    }
};


var output = JSON.parse(solc.compile(JSON.stringify(input)));

fs.ensureDirSync(buildPath); // ensure build folder exists

for (let contract in output) {
    fs.outputJSONSync(
        path.resolve(buildPath, contract + '.json'),
        output[contract]
    );
}