Executing a callback function in Swift using JavaScriptCore

Question

Executing a callback function in Swift using JavaScriptCore

Struggling to figure out how to call a Javascript Function with a callback from Swift, but it's not working as expected.

Here's what I have:

Javascript:

global.calculateWithCb = function(temp,cb){
    cb(5 * temp)
}

global.calculate = function(temp) {
    return 5 * temp
}

Swift:

let context = JSContext()
let scriptURL = NSURL(fileURLWithPath: String("XXX/bundle.js"))
let script : String = try String(contentsOfURL:scriptURL, encoding: NSUTF8StringEncoding)

var jsSource: String! = script
jsSource = "var window = this; \(jsSource)"
context.evaluateScript(jsSource)

let calculate = context.objectForKeyedSubscript("calculate")
let output = calculate.callWithArguments([40]).toNumber()

Although the calculate function is functioning correctly, I'm stuck on how to pass a block as a callback argument. I've searched extensively online for a solution but haven't found any helpful hints. Can anyone provide guidance on how to achieve this?

javascript ios swift callback javascriptcore

Answer 1

Answer №1

In order to pass a Swift block to a JSValue as an argument, you must first manually initialize the JSValue with a @convention(block) block.

let testBlock : @convention(block) (JSValue?) -> Void = { calledBackValue in
    print("calledBackValue:", calledBackValue)
}
let callback = JSValue.init(object: testBlock, in: context)
// ...
jsFunctionToCallWithCallback.call(withArguments: [42, callback])

var theJSFunction = function(val, callback) {
    // Do smt...
    callback(val);
}

Answer 2

In order to pass a Swift block to a JSValue as an argument, you must first manually initialize the JSValue with a @convention(block) block.

let testBlock : @convention(block) (JSValue?) -> Void = { calledBackValue in
    print("calledBackValue:", calledBackValue)
}
let callback = JSValue.init(object: testBlock, in: context)
// ...
jsFunctionToCallWithCallback.call(withArguments: [42, callback])

var theJSFunction = function(val, callback) {
    // Do smt...
    callback(val);
}

Executing a callback function in Swift using JavaScriptCore

Answer №1

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