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https://github.com/bnoordhuis/vime

vime, a faster vm module
https://github.com/bnoordhuis/vime

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vime, a faster vm module

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# vime, a faster vm module



## Synopsis



Execute JS code in a new VM context.



## Motivation



The [built-in vm module] is flexible but slow.  Code sometimes runs [200x

slower](https://github.com/nodejs/benchmarking/issues/75#issuecomment-262740252)

inside a vm context than outside.  Vime sacrifices some flexibility in exchange

for fast and reliable performance.



## Usage



The module exports a single function.



```js

const vime = require('vime');

const result = vime('1 + 1');

console.log(result);  // Prints "2".

```



To execute more code in the same vime context, first grab a reference to the

global object (or any other object from the context):



```js

const vime = require('vime');

const context = vime('this');

vime('var x = 1', context);

console.log(vime('x + x', context));  // Prints "2".

```



Exporting functions from the main context is done in similar fashion:



```js

const vime = require('vime');

const context = Object.assign(vime('this'), { console, require });

vime('console.log(require("./package.json"))');

```



It follows that `vime()` is not restricted to running JS code in a _new_

context, you can also execute it in the current context:



```js

const vime = require('vime');

const context = global;  // Or any object from this context.

vime('console.log("ok")', context);  // Prints "ok".

```



## Caveats



`instanceof` checks don't work across contexts because each context gets

its own copy of `Object`, `Array`, and other built-ins.



```js

const vime = require('vime');

const array = vime('[]');

console.log(Array.isArray(array));  // Prints "true".

console.log(array instanceof Array);  // Prints "false".

```



References to objects from a context keep the context alive until the last

reference goes away.  Because contexts are heavy-weight objects (a context

is a complete JS runtime), keeping many contexts around has a notable impact

on memory usage:



```js

const vime = require('vime');

console.log(process.memoryUsage().rss >>> 20);  // 25 MB on my machine.

const leak = [];

for (let i = 0; i < 100; ++i) leak.push(vime('this'));

console.log(process.memoryUsage().rss >>> 20);  // 100 MB on my machine.

```



Use [node-heapdump] or the [built-in inspector] to debug such issues.



Important note: this module is currently not designed for executing untrusted

code ("sandboxing.")  If that is an important use case for you, please file a

bug report.



## Reporting bugs



Report bugs at https://github.com/bnoordhuis/vime/issues.  Please check

existing issues first.  If possible, include a test case demonstrating

the bug.



UNIX users, please include the output of `node -v` and `uname -a`.



Windows users, please include the output of `node -v` and `winver`.



When reporting build errors, include the full terminal output from

`npm install vime` on down and the output of `g++ -v` or `clang++ -v`

(if you are a UNIX user) or the version of Visual Studio or Build Tools

(if you are a Windows user.)



## License



ISC.  See the LICENSE file in the top-level directory.



[built-in vm module]: https://nodejs.org/dist/latest-v7.x/docs/api/vm.html

[built-in inspector]: https://medium.com/@paul_irish/debugging-node-js-nightlies-with-chrome-devtools-7c4a1b95ae27

[node-heapdump]: https://github.com/bnoordhuis/node-heapdump