ES6 new syntax of Rest and Spread Operators

Rest and Spread Operators.md

Why we need rest and spread operators?

var showCollections = function(id, ...collection){
    console.log(collection instanceof Array);
};
showCollections(42, 'movies', 'music');

instanceof

The instanceof operator tests whether the prototype property of a constructor appears anywhere in the prototype chain of an object.

a demo about the propety of the instance.

function C(){}
function D() {}

var o = new C();
o instanceof C;

o instanceof D;

o instanceof Object;

C.prototype instanceof Object;
C.prototype = {};
var o2 = new C();

o2 instanceof C;
o instanceof C;

D.prototype = new C();
var o3 = new D();

o3 instanceof D;
o3 instanceof C;

var showCollections = function(id, ...collection){
    console.log( arguments.length);
}
showCollections (123, 'movies', 'music');

var showCollections = function(id, ...collection) {
    console.log(collection);
};
showCollections(42, 'movies', 'music' );

var showCollections = function(id, ...collection){};
console.log(showCollections.length);

The length property ignores the Rest Parameter.

var showCollections = function(id, ...collection){
    console.log(arguments.length);
};

showCollections(123, 'movie', 'music');

var getFirst = new Function("...args"," return args[0]");
console.log(getFirst(1,2));

The Spread Operator

Spread Operator spreads out an array and passed the values into the specified function.

It used into an arrry

let values = [300, 400, 500];
let newSet = [100, ...values, 500];

console.log(newSet);

In ES6,you have the ability to pass a function a dynamic number of parameters very easily.If you want to do this in ES5,you would have to put all the values in a data container data type like an array.

let numbers = [-25, 100, 42, -1000 ];
console.log(Math.max(...numbers,900));

function printInput(...input){
    console.log(input);
}

let input = [,,];
printInput(...input);