There are linting tools that you can and should add to your text editor of choice. Whenever I reference a variable in JS, if that variable is not assigned it highlights it as a possible error. If I define a variable or function and don't use it, that gets highlighted too. If my syntax is wrong, that gets highlighted. If my team had decided that we only want to use single quotes around strings, that gets highlighted. Even our build will complain and our tests will fail because we have incorporated linting into them. With ES6 there is no reason to have global variables anymore, so it is possible to confidently identify all these errors before the code is even run.

The language is constantly being improved while maintaining backwards compatibility. Finally it's ability to handle whatever kind of data you throw at it until you choose to check the data is a strength in an environment (web pages) where nothing is certain. You aren't sure about the data you will get from an API, from the user, you don't even know what kind of environment your code will be run in! The same code might run on the latest version of Chrome, a headless test environment, or some old version of Internet Explorer. And that is totally possible. It's all up to how you code it. And you have to get used to coding in this type of language. You can and should test your code as you go along, no need to wait to compile, you can see the results right away. Build your code to handle errors, because even if the code is perfect, the data you are working with will not be. And have lots of tests. Not only do they identify current errors in the code, but they allow you to make large changes with confidence that everything else is still working like it should.