Q:

What is ...DirectiveName mean in angular 2

What is ...DirectiveName mean in angular 2
Exp: [...ROUTER_DIRECTIVES]
When I use only  [ROUTER_DIRECTIVES] it still work, Why we add ... before

A:

I found the answer by myself, ... is Spread syntax.
Example: 
var parts = ['shoulders', 'knees'];
var lyrics = ['head', ...parts, 'and', 'toes']; // ["head", "shoulders", "knees", "and", "toes"]

See:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator 
And angular 2 understand both of it.

