Rest Parameter in ECMAScript

Demo 1

Create new Javascript file named demo1.js. This file contains code demo as below:

function myFunc(a, b, ...args) {
    console.log('Length: ' + args.length);
    console.log(args);
}
myFunc(1, 2);
myFunc(1, 2, 3, 4);

Run Demo 1

Use node demo1.js statement run code demo

Length: 0
[]

Length: 2
[ 3, 4 ]

Demo 2

Create new Javascript file named demo2.js. This file contains code demo as below:

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

console.log('Sum 1: ' + sum(3, 2));
console.log('Sum 2: ' + sum(3, 2, 6));
console.log('Sum 3: ' + sum(3, 2, 9, 10));

Run Demo 2

Use node demo2.js statement run code demo

Sum 1: 5
Sum 2: 11
Sum 3: 24

Demo 3

Create new Javascript file named demo3.js. This file contains code demo as below:

function sum(...numbers) {
    let s = 0;
    for (let number of numbers) {
        s += number;
    }
    return s;
}

console.log('Sum 1: ' + sum(3, 2));
console.log('Sum 2: ' + sum(3, 2, 6));
console.log('Sum 3: ' + sum(3, 2, 9, 10));

Run Demo 3

Use node demo3.js statement run code demo

Sum 1: 5
Sum 2: 11
Sum 3: 24

Demo 4

Create new Javascript file named demo4.js. This file contains code demo as below:

class King {

    constructor(name, country) {
        this.name = name;
        this.country = country;
    }

    getDescription() {
        return `${this.name} leads ${this.country}`;
    }

}

var details = ['Name 1', 'Country 1'];
var king = new King(...details);
console.log(king.getDescription());

Run Demo 4

Use node demo4.js statement run code demo

Name 1 leads Country 1