Babel: Function parameter types in ES6

If I write the following piece of code and transpile it through Babel (6.5.0) it works correctly.

function foo (first: string, second: number) {
    // code here
}

: string and : number are just removed from the transpiled ES5 code.

If I call the function using wrong parameter types, it does not result in any error/warning. They are informative even though do not have any functionality.

I cannot find proper information about ES6's parameter typing on internet. Is parameter typing even part of ES6?

EDIT: This question got answered in the comments below and I wrapped the official answer based on them.