How to execute Acornima's Script (AST)

[YvesHenri]

Is there a way to execute an Acornima's Script (AST)? I have a case that I'll need to traverse the AST for some validation (I'll block the usage of some JS capabilities) and it would be nice if I could reuse that AST within Jint's Engine, since I'm assuming the Engine creates an AST internally on every Engine.Execute(string), right?

[lahma]

Engine.PrepareScript and Engine.PrepareModule will give you Prepared<T> which you can feed to engine and it also includes the AST via Program property.

[YvesHenri]

Apparently, the only problem is that Acornima's parser validates the syntax before we can traverse the AST. My use case is that we need to allow scripting in JavaScript syntax, but we dont want to enable all the ECMA's features. Instead, we only need variable (only var, no let or const) and function declaration (and returns), function calls, variable references, loops (and breaks) and finally conditions, nothing else (no await, require, classes, prototypes etc etc etc). Whats the best way to achieve this other than writing a custom parser/interpreter?

[lahma]

I'm not sure I fully follow. So you want to restrict the user's syntax? Whatever you do it will go through Acornima and then can be processed with Jint. Would you like to manually create some AST to run without it being legal JS?

[YvesHenri]

I'd like to use only the most fundamental parts of JavaScript—like var, function, loops (for, while), if/else, return, and break—while avoiding more complex or implicit behaviors like new, this, await, class, prototypal inheritance, and built-in objects (Number, String, etc.). I want to keep my code simple, predictable, and free from hidden behaviors. For this, I understand I'd need to traverse the AST to find stuff like AwaitStatement, NewStatement and such.

[sebastienros]

If your intended simplified syntax is still compatible with js, you parse it, and create a visitor that will return error messages when it finds nodes it doesn't allow. If nothing fails then you can run it.

[YvesHenri]

@sebastienros the problem is that if I parse it with Esprima, it will throw errors before I can inspect the generated AST, eg:

var new = 5
console.log(new)

This throws

Unexpected token 'new' (1:6)

While:

await console.log(1)

Throws:

await is only valid in async functions and the top level bodies of modules (1:2)

At first, I wanted to create my own parser and interpreter for my custom language, but since it looks pretty much like JavaScript, I thought of using Jint (and Esprima).