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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() {} }'
var output = solc.compile(input, 1)
for (var contractName in output.contracts) {
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')
var output = solc.compileStandardWrapper(input, findImports)
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')
solc.loadRemoteVersion('latest', function (err, solcSnapshot) {
if (err) {
}
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)
Formatting old JSON assembly output
There is a helper available to format old JSON assembly output into a text familiar to earlier users of Remix IDE.
var translate = require('solc/translate')
// assemblyJSON refers to the JSON of the given assembly and sourceCode is the source of which the assembly was generated from
var output = translate.prettyPrintLegacyAssemblyJSON(assemblyJSON, sourceCode)