context.call: does not support non-global function names

[gi]

When calling a function, only global function names are supported. Functions which are properties of an object, or otherwise nested/scoped, are not supported: e.g. object.fn.

This works:

context = MiniRacer::Context.new
context.eval('bare = () => 1')
# => #<MiniRacer::JavaScriptFunction:0x00007f96e8acf798>
context.call('bare')
# => 1

This breaks:

context = MiniRacer::Context.new
context.eval('object = {}')
context.eval('object.nested = () => 1')
# => #<MiniRacer::JavaScriptFunction:0x00007f96e899d5a0>
context.call('object.nested')
# => Unknown JavaScript method invoked (MiniRacer::RuntimeError)

Environment:

• ruby: 3.0.2
• mini_racer: 0.5.0

[SamSaffron]

Nice catch, I do support fixing this, would you like to try a PR? I assume we need to be a bit more sophisticated around looking up the function.

…

On Wed, Jan 5, 2022 at 5:56 AM Zach Gianos ***@***.***> wrote: When calling a function, only global function names are supported. Functions which are properties of an object, or otherwise nested/scoped, are not supported: e.g. object.fn. This works: context = MiniRacer::Context.newcontext.eval('bare = () => 1')# => #<MiniRacer::JavaScriptFunction:0x00007f96e8acf798>context.call('bare')# => 1 This breaks: context = MiniRacer::Context.newcontext.eval('object = {}')context.eval('object.nested = () => 1')# => #<MiniRacer::JavaScriptFunction:0x00007f96e899d5a0>context.call('object.nested')# => Unknown JavaScript method invoked (MiniRacer::RuntimeError) — Reply to this email directly, view it on GitHub <#224>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAABIXPXSSWXNSPX2GPA25LUUM7FNANCNFSM5LIEHVYA> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[tisba]

While looking at #136, I noticed, that MiniRacer cannot invoke functions that are defined with const. This looks related to the original error.

require "mini_racer"
require "date"

ctx = MiniRacer::Context.new
ctx.eval("const echoFn = (obj) => obj;")
ctx.call("echoFn", "hello world!")
#  => /Users/basti/.rvm/gems/ruby-3.1.0/gems/mini_racer-0.6.2/lib/mini_racer.rb:237:in `call_unsafe': Unknown JavaScript method invoked (MiniRacer::RuntimeError)

[gi]

@tisba That is a different issue and may be by design.

As you may know, const and let define lexically scoped identifiers. Thus, it is possible that MiniRacer or V8 isolates the visibility of those identifiers between eval calls, where each evaluation could be seen as a separate lexical scope.

[gi]

The original issue here is that the string used to identify the function to call is not evaluated to lookup the function:

In Ruby,

context.call("a.b")

is interpreted in JavaScript as

this["a.b"]()

instead of

this["a"]["b"]()

[tisba]

That's a good point, @gi, thx!

For reference https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const:

Constants are block-scoped, much like variables declared using the let keyword.[…]

But what surprises me then is that the defined constant is still visible on subsequent invocations:

require "mini_racer"

ctx = MiniRacer::Context.new
ctx.eval("const foo = 42;")
a = ctx.eval("foo + 1;")
# a => 43
ctx.eval("foo = 42;")

# JavaScript at <anonymous>:1:5: TypeError: Assignment to constant variable. (MiniRacer::RuntimeError)

Since I can also use foo in subsequent #eval calls, it looks like the same scope is used every time. I think these issues are related after all and it feels like a similar lookup issue 🤔