JavascriptCore extending Swift class

Question

Created Mar ’18

Replies 3

Boosts 0

Views 1.8k

Participants 3

Is it possible to expose a swift class to JavascriptCore using JSExport and add a javascript subclass? I'm getting this weird behavior:

swift:

@objc protocol Person {

init()

func sayHi()

}

class PersonProxy: NSObject, Person {

required override init() {

super.init()

}

func sayHi() {

print("hi")

}

jsContext?.setObject(PersonProxy.self, forKeyedSubscript: "Person" as (NSCopying & NSObjectProtocol)!)

javascript:

class Employee extends Person {

constructor() {

super()

}

sayHello() {

console.log("hello")

}

var test = new Employee()

console.log("Is Employee: " + (test instanceof Employee)) // this prints "Is Employee: false"

test.sayHello() // this gives me "JS Exception: TypeError: test.sayHello is not a function"

Boost

Answer 1

ianterrell OP

Mar ’18

I'm running into something quite similar, but even without the class extension.

import JavaScriptCore
let context = JSContext()!
@objc protocol PersonJSExports: JSExport {
    static func hi() -> String
}
@objc class Person: NSObject, PersonJSExports {
    class func hi() -> String { return "hello" }
}
context.exceptionHandler = { context, exception in
    print("Custom exception handler: \(exception?.description ?? "unknown error")")
}
context.setObject(Person.self, forKeyedSubscript: "Person" as NSString)
context.evaluateScript("Person.hi()")

// Prints:
// Custom exception handler: TypeError: Person.hi is not a function. (In 'Person.hi()', 'Person.hi' is undefined)

Did you find out what the trouble was?

0

Answer 2

DTS Engineer OP

Apple

Mar ’18

How are you testing this? I tried your code and it worked for me. Specifically:

I created a new project from the macOS > Command Line Tool template.
I then replaced
```
main.swift
```
with your code.

I tweaked the last line to print the result of the evaluation.

let result = context.evaluateScript("Person.hi()")
print(result)

.

When I ran the program I saw this:
```
Optional(hello)
```
.

This is Xcode 9.2 on macOS 10.13.3.

Share and Enjoy
—
Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware

let myEmail = "eskimo" + "1" + "@apple.com"

0

Answer 3

ianterrell OP

Mar ’18

Ah, hmm! I was testing this in a Playground. It appears to work inside an application. That was surprising to me, since most of JavaScriptCore worked flawlessly in the playground. Thanks!

0