I had the same question as you,I think ,maybe your project is short of the '.js' file.
You can add the '.js' file to the project-resource , then have a try.
By the way ,In my project , It has the ',js' file,but there is still a quetion.
In my projtct,I want load a HTML that use google maps api and show maps offline ,oc course I have doemloaded the map titles .the HTML can work in any browser, such as chrome, IE ,firefox and so on,but the html doesnot work in Qt5.6.0 which I use the QWebEngineWidget class.
The error is :
js: Uncaught TypeError:google.maps.LatLng is not a function
js: Uncaught TypeError:google.maps.MAP is not a function
If you can reproduce this easily with a minimal compilable example, you should go to the bug report system to see if it's something known. If not please consider opening a new report providing that example and the guidelines to trigger the bug.