solc-js

JavaScript bindings for the Solidity compiler.

Uses the Emscripten compiled Solidity found in the solc-bin repository.

Node.js Usage

To use the latest stable version of the Solidity compiler via Node.js you can install it via npm:

npm install solc

Usage on the Command-Line

If this package is installed globally (npm install -g solc), a command-line tool called solcjs will be available.

To see all the supported features, execute:

solcjs --help

Note: this commandline interface is not compatible with solc provided by the Solidity compiler package and thus cannot be used in combination with an Ethereum client via the eth.compile.solidity() RPC method. Please refer to the Solidity compiler documentation for instructions to install solc.

Usage in Projects

From early versions

It can also be included and used in other projects:

var solc = require('solc')
var input = 'contract x { function g() {} }'
// Setting 1 as second paramateractivates the optimiser
var output = solc.compile(input, 1)
for (var contractName in output.contracts) {
	// code and ABI that are needed by web3
	console.log(contractName + ': ' + output.contracts[contractName].bytecode)
	console.log(contractName + '; ' + JSON.parse(output.contracts[contractName].interface))
}

From version 0.1.6

Starting from version 0.1.6, multiple files are supported with automatic import resolution by the compiler as follows:

var solc = require('solc')
var input = {
	'lib.sol': 'library L { function f() returns (uint) { return 7; } }',
	'cont.sol': 'import "lib.sol"; contract x { function g() { L.f(); } }'
}
var output = solc.compile({ sources: input }, 1)
for (var contractName in output.contracts)
	console.log(contractName + ': ' + output.contracts[contractName].bytecode)

Note that all input files that are imported have to be supplied, the compiler will not load any additional files on its own.

From version 0.2.1

Starting from version 0.2.1, a callback is supported to resolve missing imports as follows:

var solc = require('solc')
var input = {
	'cont.sol': 'import "lib.sol"; contract x { function g() { L.f(); } }'
}
function findImports (path) {
	if (path === 'lib.sol')
		return { contents: 'library L { function f() returns (uint) { return 7; } }' }
	else
		return { error: 'File not found' }
}
var output = solc.compile({ sources: input }, 1, findImports)
for (var contractName in output.contracts)
	console.log(contractName + ': ' + output.contracts[contractName].bytecode)

The compile() method always returns an object, which can contain errors, sources and contracts fields. errors is a list of error mesages.

From version 0.4.11

Starting from version 0.4.11 there is a new entry point named compileStandardWrapper() which supports Solidity's standard JSON input and output. It also maps old compiler output to it.

var solc = require('solc')

// 'input' is a JSON string corresponding to the "standard JSON input" as described in the link above
// 'findImports' works as described above
var output = solc.compileStandardWrapper(input, findImports)
// Ouput is a JSON string corresponding to the "standard JSON output"

There is also a direct method, compileStandard, which is only present on recent compilers and works the same way. compileStandardWrapper is preferred however because it provides the same interface for old compilers.

From version 0.4.20

Starting from version 0.4.20 a Semver compatible version number can be retrieved on every compiler release, including old ones, using the semver() method.

Using with Electron

Note: If you are using Electron, nodeIntegration is on for BrowserWindow by default. If it is on, Electron will provide a require method which will not behave as expected and this may cause calls, such as require('solc'), to fail.

To turn off nodeIntegration, use the following:

new BrowserWindow({
	webPreferences: {
		nodeIntegration: false
	}
})

Using a Legacy Version

In order to compile contracts using a specific version of Solidity, the solc.loadRemoteVersion(version, callback) method is available. This returns a new solc object that uses a version of the compiler specified.

You can also load the "binary" manually and use setupMethods to create the familiar wrapper functions described above: var solc = solc.setupMethods(require("/my/local/soljson.js")).

Using the Latest Development Snapshot

By default, the npm version is only created for releases. This prevents people from deploying contracts with non-release versions because they are less stable and harder to verify. If you would like to use the latest development snapshot (at your own risk!), you may use the following example code.

var solc = require('solc')

// getting the development snapshot
solc.loadRemoteVersion('latest', function (err, solcSnapshot) {
	if (err) {
		// An error was encountered, display and quit
	}
	var output = solcSnapshot.compile("contract t { function g() {} }", 1)
})

Linking Bytecode

When using libraries, the resulting bytecode will contain placeholders for the real addresses of the referenced libraries. These have to be updated, via a process called linking, before deploying the contract.

The linker module (require('solc/linker')) offers helpers to accomplish this.

The linkBytecode method provides a simple helper for linking:

var linker = require('solc/linker')

bytecode = linker.linkBytecode(bytecode, { 'MyLibrary': '0x123456...' })

(Note: linkBytecode is also exposed via solc as solc.linkBytecode, but this usage is deprecated.)

As of Solidity 0.4.11 the compiler supports standard JSON input and output which outputs a link references map. This gives a map of library names to offsets in the bytecode to replace the addresses at. It also doesn't have the limitation on library file and contract name lengths.

There is a method available in the linker module called findLinkReferences which can find such link references in bytecode produced by an older compiler:

var linker = require('solc/linker')

var linkReferences = linker.findLinkReferences(bytecode)

Updating the ABI

The ABI generated by Solidity versions can differ slightly, due to new features introduced. There is a tool included which aims to translate the ABI generated by an older Solidity version to conform to the latest standard.

It can be used as:

var abi = require('solc/abi')

var inputABI = [{"constant":false,"inputs":[],"name":"hello","outputs":[{"name":"","type":"string"}],"payable":false,"type":"function"}]
var outputABI = abi.update('0.3.6', inputABI)
// Output contains: [{"constant":false,"inputs":[],"name":"hello","outputs":[{"name":"","type":"string"}],"payable":true,"type":"function"},{"type":"fallback","payable":true}]