Usage of rest parameter and spread operator in javascript

Question

What\'s the usage of rest parameter that will be added in ECMAScript 6?

For example, in ECMAScript 5 you can do the following to get an array of parameters starting

Answer 1

Is the difference between them is just syntax or there's a performance issue?

Both, and more...

Rest parameters:

1. Are a known idiom in other languages (Ruby, Python).
2. Are esier to read and maintain (vs. slice).
3. Are easier to understand for beginners.
4. Can (and likely will) result in better performance, since engines can optimize.
5. Are tool friendlier, as they can be analyzed statically.