Creating your own custom Syntax Errors in Javascript! (SyntaxError) 

This is very useful in .net, so I assume it will be useful in javascript - if you have a large JS project, it's useful for bubbling up the errors through the function. So you have your "main" function at the top with the try catch, and then sub functions in the try, if they error you then throw them errors, which then bubble up to the main function and that then can display / log the error to the user / developer - helps to cleanly exit out of the sub functions. Hope this makes sense.

I think so, but would they be syntax errors?

it is useful in constructor assign to a data field in which is required. constructor ({ dataField = isRequired('dataField')}) { this.dataField = dataField } ... const isRequired = name => { throw new SyntaxError(`${name} is required.` }