Isolated Runtime Core

Provides a runtime environment for executing Javascript code loaded from a provided file, within a controlled (isolated) context. The core functionality of this module is provided by the CodeRunner class, which takes the root path in which the code to be run resides, and the file in which source code of the functions to exectute is stored.

What does "isolated" actually mean?

The isolation-level provided by this library has several aspects:

1. A function cannot require() any module other than ones pre-defined upon creating a CodeRunner instance.
2. A function cannot access files located in the hosting process in which CodeRunner is being used (thus executing process.exit(1) will result in an exception as process will be undefined
3. Different invocations of the same function cannot share any state with each other.

Isolation illustrated

Once an instance of CodeRunner is created, it can be used to execute any number of calls to the functions within the provided file, but some restrictions apply - each run is isolated from a preceding or consequent run, meaning that if your function modifies the global scope to save some state, those changes will not be persisted:

// my-module/index.js
 
function foo(n) {
  global.bar = (global.bar || 0) + n
  return global.bar
}

// index.js
 
global.bar = 0
 
const runner = new CodeRunner({ root: '/absolute/path/to/root', file: 'my-module.js' })
 
const result1 = await runner.run({
  funcName: 'foo',
  args: [1]
})
 
console.log(result1) // 1 
console.log(global.bar) // 0
 
const result2 = await runner.run({
  funcName: 'foo',
  args: [2]
})
 
console.log(result2) // 2
console.log(global.bar) // 0

Note that the assignments made to global.bar did not change its value, and the functions get its value as 0 every time.

API

CodeRunner({
  root: string;
  file: string;
  onConsole?: (method: string, ...args: any[]) => void;
  sourceExtensions?: string[];
  compiler?: (code: string) => string;
  external?: string[];
  whitelistedPaths?: string[];
  resolve?: (moduleName: string) => string;
})

• root - an absolute path containing the code-file provided via the file argument (e.g., /var/usr/my-code)
• file - a file-name to run the code from when the run() method is being called. (e.g., index.js) onConsole - a callback to invoke for every call to console.<method> performed in the executed code. Since console.<method> calls are not redirected to the stdout stream of the parent process hosting CodeRunner, onConsole provides a way to act upon those calls and possibly write them the parent process' stdout.
• onConsole is invoked with two arguments: (method, ...args), where method is the name of the orignally method invoked on console from the executed function, and args are the arguments passed to that console method.
• sourceExtensions - allows requiring files with extensions other than .js, by passing an array of the allows extensions:. e.g.: ['.js1', '.xyz']
• compiler - an optional function to transform the code prior to execution. Takes a single argument - code, that holds the source code to transpile, and expected to return the transpiled code as a string.
• external - if you wish to allow your code to require() modules that are not relative to the function being executed, those module names can passed through this array. e.g.: ['fs', 'lodash']
• whitelistedPaths - a list of absolute paths to allow loading relative modules from. Required since loading relative modules is restricted to paths stemming from the root folder by default. e.g: ['/var/usr/a', '/b/c/d']
• resolve - an optional function to provide custom module-resolving logic, in case the traditional lookup logic implemented in Node needs to be extended or restricted. Once a module require()-ed by the executed-code cannot be found, the requested module id (path / name) is passed to this function and it's expected to return a string with the absolute path to the module file, or null if the lookup did not succeed.

codeRunner.run({
  funcName: string;
  args: any[];
  context?: object;
  running?: () => void;
  resolveArguments?: (args: any[]) => any[];
})

• funcName - name of the function that should run.
• args - an array of arguments to pass to the function.
• context - optional global context to be injected to the sandbox.
• running - optional callback, which will be called after the function was found, but before it was run.
• resolveArguments - optional function, will be applied on the arguments before passing them to the function.