Rest Parameters:

 

In ES5, when you don't know how many paramters will be passed in, you can use arguments:

let sum = function(){    let result = 0;    for(let i = 0; i < arguments.length; i++){        result += arguments[i];    }    return result;}let result = sum(1,2,3);

 

In ES6, you can use Rest params:

let sum = function(...numbers){        let result = 0;    for(let i = 0; i < numbers.length; i++){        result += numbers[i];    }    return result;};

 

describe("rest paramters", function(){    it("is like varargs", function(){            let doWork = function(name, ...numbers){                    let result = 0;            numbers.forEach(function(n){                result += n;            });                        return result;        };                let result = doWork("Scott", 1,,2,3);        expect(result).toBe(6);    });});

 

...Spread:

It looks the same as Rest Parameters, Spread uses to spread an array.

it("should sum up", function(){    let doWork = function(x,y,z){        return x+y+z;    };        expect(doWork(...[1,2,3])).toBe(6);});