npm solc: AssertionError [ERR_ASSERTION]: Invalid callback specified

Question

I am trying to compile solidity smart contract using npm solc. I tried to follow different examples. Link to example: https://medium.com/coinmonks/how-to-compile-a-solidity-smart-contract-using-node-js-51ea7c6bf440

I wrote my code like following:

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



const helloPath = path.resolve(__dirname, 'contracts', 'hello.sol');
console.log("First" + helloPath);
const source = fs.readFileSync(helloPath, 'UTF-8');
console.log("Second" + source);
console.log(solc.compile(source, 1));

I am getting following error when running the above code.

AssertionError [ERR_ASSERTION]: Invalid callback specified.
    at wrapCallback (C:\Users\mouazzamj058\solc_example\node_modules\solc\wrapper.js:16:5)
    at runWithReadCallback (C:\Users\mouazzamj058\solc_example\node_modules\solc\wrapper.js:37:42)
    at compileStandard (C:\Users\mouazzamj058\solc_example\node_modules\solc\wrapper.js:78:14)
    at Object.compileStandardWrapper (C:\Users\mouazzamj058\solc_example\node_modules\solc\wrapper.js:85:14)
    at Object.<anonymous> (C:\Users\mouazzamj058\solc_example\example.js:4:19)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)

Please help.

Answer 1

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]

Answer 2

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))));

Answer 3

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;