JavaScript is written in C++, including engines like Spider Monkey, V8, Chakra, etc. That is, JavaScript codes are compiled to machine codes, but C++ binding is used in runtime between the browser and the engine.
Since browsers only support JavaScript, other programming languages can be transpiled to JavaScript before the C++ binding can be done successfully.
Codes can now be transpiled from languages like TypeScript, Dart, etc. to JavaScript then compiled to machine codes in the JavaScript engine
Below are alternative languages to JavaScript:
It is advisable to know JavaScript fully well before learning other alternatives to JavaScript.