How do I get Swift to run a Webview Javascript?

I would like to run the following Javascript in the webview in the UIButton written in Swift, but could you help me?

Javascript side

function show()
{
alert("Run JavaScript";←I want to do this on Swift
}

Swift side import UIKit
import JavaScriptCore

classViewController:UIViewController, UIWebViewDelegate {

var webView:UIWebView=UIWebView()

}

button.addTarget(self, action: "pushBtn:", forControlEvents: .TouchUpInside)

func pushBtn (sender:AnyObject) {

// Now I want to write a code to call the function show() of the webview.

    // Alert notes in Swift below
    let alert=UIAlertView()
    alert.title="Swift"
    alert.message="Alert on Swift"
    alert.addButtonWithTitle("OK")
    alert.show()
}