wasm: improve the specialHtmlTargets test

It can actually be undefined, so test for that before checking
the object type.

This fixes the asyncify build.

Pick-to: 6.4
Change-Id: I5a6a0bc60c153290c35c20242400c59cd1312403
Reviewed-by: Aleksandr Reviakin <aleksandr.reviakin@qt.io>
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/plugins/platforms/wasm/qwasmscreen.cpp b/src/plugins/platforms/wasm/qwasmscreen.cpp
index ad9e5b1f5a..42ca608da1 100644
--- a/src/plugins/platforms/wasm/qwasmscreen.cpp
+++ b/src/plugins/platforms/wasm/qwasmscreen.cpp
@@ -172,10 +172,14 @@ std::string QWasmScreen::canvasSpecialHtmlTargetId() const
 bool QWasmScreen::hasSpecialHtmlTargets() const
 {
     static bool gotIt = []{
-        // specialHTMLTargets is a JavaScript Array if available. Note that it is
-        // an abort() function if not, so a simple isUndefined() test won't work here.
-        return emscripten::val::module_property("specialHTMLTargets")
-               ["constructor"]["name"].as<std::string>() == std::string("Array");
+        // Enable use of specialHTMLTargets, if available
+        emscripten::val htmlTargets = emscripten::val::module_property("specialHTMLTargets");
+        if (htmlTargets.isUndefined())
+            return false;
+
+        // Check that the object has the expected type - it can also be
+        // defined as an abort() function which prints an error on usage.
+        return htmlTargets["constructor"]["name"].as<std::string>() == std::string("Array");
     }();
     return gotIt;
 }