Yea, I mean the problem is. If you have a function that expects a number parameter. In Typescript, the compiler won't let you do this someFunction('a'), so yo

Yea, I mean the problem is. If you have a function that expects a number parameter. In Typescript, the compiler won't let you do this someFunction('a'), so you never have to worry about handling this. But, if it is in javascript, then someone can call the function like that. So in javascript, you might have a test that ensures that the function handles this gracefully. You obviously don't have to have that test, but you will have your app blow up later down the line, if someone adds a call like that. So, testing does occur at times for these types of things. You might not have done it ever, but there are certainly devs who have, myself included.