A sample project using Kotlin for backend code as well as front-end JavaScript code.
Open IntelliJ IDEA and File > Open navigate to the directory of the project and select the build.gradle file of the root directory.
After the project is setup, Build > Build Project.
Right-click on kotlinbackend/.../kotlin/Main.kt and select Run 'MainKt'
Then, right-click on out/production/kotlinfrontend/index.html and select Open in browser. It eveything works, you should see a page with some output from the API call.
You can call the API's directly by openinng http://localhost:8080/api/ping in your browser. You can additionally call pass a path parameter http://localhost:8080/api/ping/3.
You can find more details on my Medium blog Building a fullstack web-app in Kotlin