Example showing how to allow a Swift class to be instantiated via a 'new' in Javascript.

js_instantiates_swift_class.swift

// Swift 5.0 + Javascript
// How to use 'new <classtype>' in Javascript to instantiate a Swift object (from JavaScriptCore).
//
// I couldn't find this clearly documented in any one place.
//
// By Andrew Kingdom
// MIT license
//
@objc
public protocol SampleProtocol: JSExport {
    
    func message(_ text:String)
    
//    static func createSample(_ name:AnyObject) -> Sample
    static func create() -> Sample
    func initSample() -> Sample  // 'new' -- it seems this function name must be init followed by the class name.
}

@objc
open class Sample : NSObject, SampleProtocol {
    
    var old: String = ""
    
    public func message(_ text: String) {
        print("---")
        print(old)
        print(text)
        old = text
    }
    
//    public static func createSample(_ name: AnyObject) -> Sample {
//        return Sample()  // i
//    }
    
    public static func create() -> Sample {
        return Sample()
    }
    
    public func initSample() -> Sample {
        return self
    }
    
}

class Test {
    public static func test() {

        if let context = JSContext() {
            context.setObject(Sample.self,
                              forKeyedSubscript: "Sample" as NSString)
            context.evaluateScript("""
                   var sample = new Sample();
                   sample.message('Hi 🌏');
            """)
        }
    }
}