Evaluating Javascript using WKWebView in iOS

Sample of page loaded in web view:

      function getWindowInfo() {
          return {
              width: window.innerWidth || document.body.clientWidth,
              height: window.innerHeight || document.body.clientHeight

In a UIView or UIViewController:

import WebKit

// Enable Javascript in web view
let config = WKWebViewConfiguration()
let prefs = WKPreferences()
prefs.javaScriptEnabled = true
config.preferences = prefs

// Instantiate web view. Use self.view.bounds in a UIViewController.
var webView: WKWebView = WKWebView(frame: self.bounds, configuration: config)                

// Load page in web view
let url = "https://example.com/test.html"
let webViewUrl = URL(string: url)!
webView.load(URLRequest(url: webViewUrl))

// Run inline Javascript or call a function on the page loaded in the web view
let script = "getWindowInfo();"
webView.evaluateJavaScript(script, completionHandler: { (result, error) in
    // result is the value of the final statement in the injected javascript
    // if script is "var x = 1; x++;", result will be 2

    // Do some error checking
    if (error != nil || result == nil) {

    // If the Javascript function returns an object, cast it into a Dictionary
    let dict = result as! [String:AnyObject]

    // Print the key-value pairs in the dictionary
    for (key, value) in dict {
        print("\(key) : \(value)")