JavaScript from Swift

GeoWrapper.swift

import Foundation
import JavaScriptCore

public class GeoWrapper {
    var jsContext: JSContext

    public init?() {
        jsContext = JSContext()
        jsContext.exceptionHandler = { NSLog("ERROR: '%@'", $1) }
        
        if let path = NSBundle(forClass:GeoWrapper.self).pathForResource("GeoFunctions", ofType: "js") {
            let content = NSString(contentsOfFile: path, encoding: NSUTF8StringEncoding, error: nil)
            let jsval = jsContext.evaluateScript(content)
        } else {
            return nil
        }
    }
    
    public func convertOSGridRefToWSGS84(gridref: String) -> String? {
        if let jsFunction = jsContext.objectForKeyedSubscript("convert") {
            if let value = jsFunction.callWithArguments([ gridref ]) {
                return value.toString()
            }
        }
        return nil
    }
}