SentimentAnalyzer.swift

    /**
         Analyze the sentiment of a given English sentence.
 
         - Parameters:
             - sentence: The sentence to analyze
             - completion: The block to be called on the main thread upon completion
             - score: The sentiment score
     */
    func analyze(_ sentence: String, completion: @escaping (_ score: Int) -> Void) {
        // Run this asynchronously in the background
        DispatchQueue.global(qos: .userInitiated).async {
            var score = 0
            let jsModule = self.context.objectForKeyedSubscript("Sentimentalist")
            let jsAnalyzer = jsModule?.objectForKeyedSubscript("Analyzer")
            
            // In the JSContext global values can be accessed through `objectForKeyedSubscript`.
            // In Objective-C you can actually write `context[@"analyze"]` but unfortunately that's
            // not possible in Swift yet.
            if let result = jsAnalyzer?.objectForKeyedSubscript("analyze").call(withArguments: [sentence]) {
                score = Int(result.toInt32())
            }
            
            // Call the completion block on the main thread
            DispatchQueue.main.async {
                completion(score)
            }
        }
    }