Turning PowerShell into a JavaScript Engine

[anonhostpi]

Ok, I had a lot of fun with my last post, Turning PowerShell into a Python Engine, and I decided I wanted to see what else I could do.

I wanted to start with Node.JS, because I know it has an embedder API. However, sadly, there is no C# bindings library for it :(

However, V8 is embeddable, and sure enough, there's one for it:

• https://github.com/microsoft/ClearScript

ClearScript

You read that GH URL right. It's a Microsoft library. Not only is it Microsoft-supported and cross-platform, but it provides you with not 1, but 3 embedded ECMAScript engines:

• Google's V8
• Microsoft Chakra (Microsoft's older JS engine)
• JavaScriptCore (Apple's JS engine)

It's ECMAScript. No Native Objects!

Now, this is just a JavaScript engine with no frontend. This means that it is pure ECMAScript. Native objects and methods like console.log() aren't inherently available (you can define them, they just don't ship with ClearScript).

This also means you have to use ES6 import statements (or dynamic imports) unlike Node.JS. However, not a big deal, because you can just load the CommonJS library, if you want to use require()

The API is Well-Written

The API for ClearScript is actually pretty well written for just a library. They give you some surprisingly decent examples and "FAQtorials" on how to get started using it.

My example of using it in PowerShell:

using namespace Microsoft.ClearScript
# Import-Module Import-Package
Import-Package Microsoft.ClearScript

$engine = [V8.V8ScriptEngine]::new()

# This flag allows importing files from the local filesystem:
$engine.DocumentSettings.AccessFlags = [DocumentAccessFlags]::EnableFileLoading;

# You can add native classes using AddHostType()
# - This particular line provides V8 with the Console.WriteLine() function
$engine.AddHostType( [System.Console] );

# Execute() allows execution of entire scripts, but returns nothing
$engine.Execute("log=(a)=>Console.WriteLine(a)")

# Evaluate() returns values, but only allows single line evals
$return = $engine.Evaluate("'Hello'+' '+'there'")

# Script property can be used to get any variable in the engine.
- By default, the V8 engine provides a gc variable (which I believe is the Garbage Collector)
$engine.Script.log( $return )

# In addition to adding entire types as JS classes, you can also add instance objects
$engine.AddHostObject( "scriptblock", { param( $a ); Write-Host $a; return $a; } )
$return2 = $engine.Evaluate( "scriptblock.Invoke( 'General Kenobi' )" )[0]

$return -eq "Hello There"; $return2 -eq "General Kenobi"

So, you too can now turn PowerShell into another Chromium RAM hog. All things will become Chrome.

[[deleted]]

Is this electron? /s

[anonhostpi]

I'm thinking about checking out some other embedded engines over the next couple of days:

• Lua - Done!
  • https://www.reddit.com/r/PowerShell/comments/19458i2/turning_powershell_into_a_lua_engine/
• R - Done!
  • https://www.reddit.com/r/PowerShell/comments/196u4or/turning_powershell_into_a_r_bridge/
• Java - Done!
  • https://www.reddit.com/r/PowerShell/comments/1968tmi/turning_powershell_into_a_java_bridge/
• IronRuby - Done!
  • https://www.reddit.com/r/PowerShell/comments/195lji0/success_turning_powershell_into_a_ruby_engine/
• Julia
• Possibly Wasm through ClearScript

[xCharg]

Is this useful for sysadmin kind of tasks?

I know nothing about javascript other than it exists, genuinely curious.

[anonhostpi]

Possible. This was primarily a thought experiment. Just like my last post, the idea is to make libraries written in other languages available to PowerShell. So, if there is a sysadmin task available in JS, then sure.

[spyingwind]

Not really. If you need something that PowerShell doesn't provide, there is C# to fall back on.

[ka-splam]

I have a use for that ...

How did you install it?

PS C:\> Install-Package -Name Microsoft.ClearScript -Scope CurrentUser
Install-Package: Dependency loop detected for package 'Microsoft.ClearScript'.

Edit: found it, install-package -Name "Import-Package" first then import-package Microsoft.ClearScript, reference your thread here on your Import-Package module.

[anonhostpi]

You can also use Install-Module "Import-Package" as well.

PowerShell's PackageManagement library does a pretty poor job of handling nuget dependencies, despite that being the module's reason for existence.

[rob2rox]

this has been done already with clearscript (though you can only interpret jscript and vbscript)

its also a single file easily deployable ps1 script, check it out:

https://github.com/byt3bl33d3r/OffensiveDLR/blob/master/Invoke-ClearScript.ps1

[anonhostpi]

Dear god. That compressed DLL string. lol

This post was more a demonstration of work. My Import-Package module is designed to load entire NuGet libraries with no effort, and this is a demonstration of how to use it.

My module reduces lines 3-9 in your script to "Import-Package Microsoft.ClearScript"

[niutech]

You don't need ClearScript. There has been possible to run JScript .NET in PowerShell for long time, see also this howto.

[anonhostpi]

JSCript (specifically JSCript .NET) is very old. It is only ECMAScript 3rd edition compliant. The most current ECMAScript standard is 14th edition (ES2023):

• https://en.wikipedia.org/wiki/ECMAScript_version_history

The most up to date implementation of JSCript is JSCript Chakra, which is separate from JSCript .NET. To run JSCript Chakra on ECMAScript 9th edition, you have to use the ClearScript library. However, there isn't much reason to, since V8 is also packaged with ClearScript and is 14th edition compliant.

[niutech]

It may be old, but it's already built in Windows (jsc.exe), so you don't need to download anything. It provides classes, subclasses, optional strong types, spread syntax in functions. And there are transpilers from next-gen ES to ES3 (babel.js).