To close this series, I wanted to share a few additional bits related to webview, but not necessarily related to one another!

First, in the previous post I showed how to wrap some of the webview’s capture methods in a promise. The same thing is easy to do with invokeScriptAsync, where the promise is fulfilled with the value returned from the webview’s script:

functon callWebviewScript(webview, targetFunction, argsIn) {
return new WinJS.Promise(function (cd, ed) {
var op = webview.invokeScriptAsync(targetFunction, argsIn);

        op.oncomplete = function (args) {;
//Return value from the invoked function (always a string) is in

op.onerror = function (e) { ed(e); };

This kind of structure helps you remember the necessary call to start at the end.

With invokeScriptAsync, be aware that the result you pass back must be a string, otherwise you’ll get an empty string.

In the callWebviewScript function above, note that targetFunction can be set to “eval” and argsIn to whatever script string you want to evaluate–meaning that the webview doesn’t necessarily have to have a named function inside it. Just remember that the result of that eval must again be a string.

The next little tip is just knowing that webview cache cookies and other content just like the browser, even if you remove the webview from the DOM and let it get garbage collected. There aren’t facilities to clear information that’s cached in the webview, though you might be able to achieve this through the Windows.Web.HttpClient API instead.

Lastly, the webview has a characteristic that if you overlay another element on a webview that has 100% opacity, the webview will go black as it fails “layer candidacy” as it’s called. The same thing happens with an overlay element with 0% opacity. (See under “Unsupported Scenarios” section for the description of scenarios where it fails layer candidacy.)

If, however, the overlay element’s style has an opacity of anything other than 1 or 0, like 0.9999 or 0.0001, then the webview is happy. It’s an odd behavior, but a good one to know about.

One Comment

  1. Posted October 9, 2014 at 5:17 am | Permalink

    Very nice blog post. I certainly love this site. Thanks!