Unfortunately, most of the SoC devices are based on older WebKit (usually version <50). Because of that, you cannot use modern JS syntax (read more on ECMAscript).
We strongly recommend to transpile your code and avoid using polyfills. If you have to use polyfills we recommend using Babel.JS.
Automated transpilation in single file Applet via Web Editor
In order to use advanced Javascript’s features and syntax, you need to either transpile your code to ES5 or use polyfills. Javascript inside the Applet Web Editor can be transpiled automatically if you use
<script type="application/ecmascript"></script>
CLI-based Applet development
While developing on your device, you can easily add Babel.js as a transpilator of choice into your project and use it during building your code.
Check browser versions sorted by platforms
Here is a list of supported devices along with their browser versions.