js-vm

js-vm

Installation

Install this package using NPM:

npm install js-vm

What is js-vm?

js-vm is highly secure, fully compatible ECMAScript 5 implementation of the Node.js VM API. It may be used as a vm shim in webpack.

js-vm is designed with high demands in efficiency and security.

• Code is transpiled only on the basis on native RegExp tokenization and no AST is created, increasing speed by a factor of some 10K.
• Security measures are designed to be widely immune to client-specific or future extensions of the grammar of the script language (ECMAScript). The package relies only on standardized ES5 features, leading to a best possible predictability and assessibility of security aspects.

What makes it fast?

js-vm executes scripts subsequently in the same global scope. No iframe or Web Worker is instantiated at runtime and execution is carried out purely by means of eval execution of RegExp-transpiled code.

To achieve this, from the perspective of an executed script, built-in properties of the global object are frozen. Any modifications on properties or sub-properties of built-in objects (such as Object.prototype.toString = function () { }) will not have any effect (see the behavior of Object.freeze()).

Considering the modification of built-in prototypes an anti-pattern in a modern modularized ECMAScript ecosystem, we regard this increased strictness as an acceptable measure that does not affect code quality but on the contrary.

js-vm will attempt to create a separate global scope (i.e., by means of an iframe or Node.js' native vm) as a target of its code execution. If such a measure is not available, however (e.g., in a Web Worker), built-in objects, execution of the host environment appear as frozen, too.

Limitations with respect vm

• All scripts run in strict mode (or an unspecified superset, if unsupported).
• Built-in objects (Object, Array, Date etc.) and their prototypes are immutable. This includes properties such as RegExp.lastMatch, which normally are altered dynamically.

Extensions over vm

• The timeout option is not only applied to the main operation, but also on subsequently executed events, timed functions etc.

Usage

var vm = require('js-vm');
var sandbox = { console };

vm.runInNewContext('console.log("Hello world")', sandbox);

See the Node.js vm documentation.

License

© 2016 Filip Dalüge, all rights reserved.