Support for async functions/Promises in ExecuteScript

[Kitiara]

Is there a way to read data as text from a blob url ? I've tried executing async/await javascript but i couldn't make it work for blobs.

AB#28965236

[champnic]

Can you share some more details about your scenario/code? Are you doing this entirely on the javascript side? Does you code work in the browser (not in a webview)?

[Kitiara]

Can you share some more details about your scenario/code? Are you doing this entirely on the javascript side? Does you code work in the browser (not in a webview)?

wstring script(L"(() => {"
L"async function fnc() {"
    L"let bl = await fetch(document.getElementById('test').href).then(r => r.blob());"
    L"var reader = new FileReader;"
    L"reader.readAsText(bl);"
    L"let promise = new Promise((res, rej) => {"
        L"setTimeout(() => res(reader.result), 100)"
    L"});"

    L"return await promise;"
L"}"

L"return fnc().then(function(value) {"
    L"return value; });"
L"})();");

webview->ExecuteScript(script.c_str(), Callback<ICoreWebView2ExecuteScriptCompletedHandler>(
	[](HRESULT errorCode, PCWSTR result) -> HRESULT {
		MessageBox(nullptr, result, L"ExecuteScript Result", MB_OK);
	return S_OK;
}).Get());

The result is always '{}'. I have tested the javascript on the console side of browser and it seems to be working just fine but not in webview2 ??

[champnic]

A quirk of ExecuteScript (and the underlying CDP call) is that objects are often just returned as "{}". Try wrapping your return value in a .toString().

[champnic]

We're tracking improvements here as part of #105.

[Kitiara]

A quirk of ExecuteScript (and the underlying CDP call) is that objects are often just returned as "{}". Try wrapping your return value in a .toString().

Async functions always return promises, .toString has just proved that. I couldn't get any data no matter what i try.
But i managed to get some data by using ajax. Check this out:

    wstring jquery(L"var jqry = document.createElement('script');"
    L"jqry.src = 'https://code.jquery.com/jquery-3.3.1.min.js';"
    L"document.getElementsByTagName('head')[0].appendChild(jqry);");
    webview->ExecuteScript(jquery.c_str(), Callback<ICoreWebView2ExecuteScriptCompletedHandler>(
        [webview](HRESULT errorCode, PCWSTR result) -> HRESULT {
        return S_OK;
    }).Get());
    Sleep(500);
    wstring script(L"jQuery.noConflict();"
    L"function testAjax() {"
    L"var result='';"
    L"jQuery.ajax({"
        L"url:document.getElementById('test').href,"
            L"async: false,"
            L"success:function(data) {"
                L"result = data; "
            L"}"
            L"});"
        L"return result;"
    L"}"
    L"(() => {"
        L"return testAjax()"
    L"})();");
    webview->ExecuteScript(script.c_str(), Callback<ICoreWebView2ExecuteScriptCompletedHandler>(
        [webview](HRESULT errorCode, LPCWSTR result) -> HRESULT {
            wcout << wstring(result).c_str() << endl;

        return S_OK;
    }).Get());

This way i'm getting some data but not all of it. On the other hand, i have tested this ajax script on the console side of the browser and it worked there. Any ideas ?

[champnic]

Ah, I understand now. We don't currently support async function results in ExecuteScript. It looks like there's a path forwards for implementing support there, so I'll open a feature request on our side to track that.

As a workaround, you should be able to use window.chrome.webview.postMessage(data) and add_WebMessageReceived to get out the data from inside your "then" function with the result. Let me know if that work.

[Kitiara]

The ajax method is working. I noticed that certain unicodes are causing wcout to fail. I managed to print whole data by using
wprintf(L"%ls\n", result);
But i've found something strange. If you remove or replace null characters from javascript side then result of ExecuteScript become completely NULL.

[champnic]

I believe the ajax is working because you are making it a synchronous call - I don't think we'd recommend this, as it will block the web code while executing. postMessage when the async calls are complete is preferred.

Can you share the code that is doing the character replacement? When you say NULL do you mean the return string is "null" or that the return string is a nullptr/NULL/0x0?

[Kitiara]

I believe the ajax is working because you are making it a synchronous call - I don't think we'd recommend this, as it will block the web code while executing. postMessage when the async calls are complete is preferred.

I don't need async for the project i'm working on, so it's ok for me.

Can you share the code that is doing the character replacement? When you say NULL do you mean the return string is "null" or that the return string is a nullptr/NULL/0x0?

I mean the return string is "null". Replacing or removing any '\u0000' is causing this phenomenon.

return result.replace(/[\u0000]/g, 'X');

[champnic]

A "null" string can be returned when the javascript object is undefined, there's an exception in the script, or if there's an error in trying to serialize the result using JSON. I'm not sure why removing the null character would cause those. Can you confirm that code works in the console/browser?

[Kitiara]

A "null" string can be returned when the javascript object is undefined, there's an exception in the script, or if there's an error in trying to serialize the result using JSON. I'm not sure why removing the null character would cause those. Can you confirm that code works in the console/browser?

Yes, it is working without any problem.

[champnic]

Are you able to share what the result string is before and after the replacement? If you just use a static string (not from the server) is there some minimal string that reproduces the problem so we can take a look on our end?

[Kitiara]

It's not a static string. The result i'm getting is constantly changing but it's pattern is always the same and i'm always getting null after the replacement of the null character. So you should be able to reproduce the problem. Here it is:
Original text: before.txt
Expected outcome: after.txt