Inspired by the ExpressibleByNilLiteral protocol, I came up with this subscript-based JSValueConvertible protocol:

public protocol JSValueConvertible {
    subscript(jsValue _: ()) -> JSValue { get }
}

extension JSValue {
    public init(from convertible: JSValueConvertible) {
        self = convertible[jsValue: ()]
    }
}

Alright, the tests are still failing because it seems like I can’t have Array conform to JSValueConvertible when either Element: JSValueConvertible or Element == JSValueConvertible :(

Any suggestions?

Update: I’ve replaced all the function call/new logic with this pattern:

// idiomatic JS version on next line
foo()
foo()

foo(arg1, arg2, arg3)
foo(arg1, arg2, arg3)

foo(args: [arg1, arg2, arg3])
foo(...[arg1, arg2, arg3])

foo(this: bar)
foo.call(bar)

foo(this: bar, arg1, arg2, arg3)
foo.call(bar, arg1, arg2, arg3)

foo(this: bar, args: [arg1, arg2, arg3])
foo.apply(bar,  [arg1, arg2, arg3])

foo(new: arg1, arg2, arg3)
new foo(arg1, arg2, arg3)

foo(.new, args: [arg1, arg2, arg3])
new foo(...[arg1, arg2, arg3])

foo(.new)
new foo()

The last two I’m a little uncertain of.

One last change I was going to make was changing the instanceof function to an operator. I tried it out with << which isn’t super clear.

It seems Swift doesn’t allow letters in operators, so instanceof is out. There are a ton of Unicode characters allowed but the only ASCII ones are !%&*+-/<=>?^|~. Maybe <<? or <==?

Sorry, I didn't take a look much now, but could you ignore .swiftpm directory?

Sorry for late response. I basically agree with deprecating get and set and provide subscript.

But on second thought, new and instanceof are not natural and not swifty interface.

This library provides JavaScript like APIs but also they should be swifty.

I think instanceof, new and jsValue are not common naming as members and if users want to use those names, they can use subscript accessor instead.

I disagree that APIs become unnatural caring about edge cases.

Good point! I reverted those changes, so now the last few samples look like this:

foo.new(arg1, arg2, arg3)
new foo(arg1, arg2, arg3)

foo.new(args: [arg1, arg2, arg3])
new foo(...[arg1, arg2, arg3])

foo.new()
new foo()

Additionally, I changed the JSValue code back to using .jsValue() and changed instanceof to add the method isInstanceOf.

Ah, did a quick GitHub search and isInstanceOf seems to be somewhat common. Should I switch back to the slightly-less-readable name option instanceof?