Javascript : Destructuring

With the help of destructuring we can unpack values from Arrays and objects into variables directly.
It's vary common to initialize a variable form object property or array like:

let test1=arr[0], test2=arr[1] or 
let name=customer.name,etc.
Below examples will be helpful to understand Destructing in Javascript.

//array destructuring 

let arr = [90, 300, 930, 200];

[j, k] = arr;

console.log(j + " " + k);

// ... (rest operator)

[l, m, ...p] = arr;

console.log(l + " " + m);

console.log(typeof p + " " + p);

//************ object destructring ************:

//Example 1:

let { a, b } = { a: 10, b: 30, c: 90 };

console.log(a + " " + b);

//Exaple 2: object function destrucring

let obj = {

    write: function () {

        console.log("hello");

    }

}

let { write } = obj; 

write();

//Destructuring with function argument

// Normally we work with object like below

let obj2 = {

    firstname: "nirnajan"

}

function WriteToConsole(val) {

    console.log(val);

}

WriteToConsole(obj2.firstname);//rsult:niranjan

//Destructuring : instead of passing object we can extract param directly

function WriteToConsole2({ firstname }) {

    console.log(firstname);

}

WriteToConsole2(obj2);

//Some complex (nested object)destructuring examples

let customer = {

    firstName: "abc",

    lastName: "bcd",

    Order: [{

        orderDate: '12/12/2020',

        orderId: 1

    }],

}

// To destructing from array within object

let { firstName, Order: [{ orderId }] } = customer;

console.log(firstName + "****" + orderId);

//another example:

var user = {

    id: 42,

    displayName: 'jdoe',

    fullName: {

        firstName: 'John',

        lastName: 'Doe'

    }

};

let { displayName, fullName: { firstName: name } } = user;

//here firstName:name means renaming 'firstName to name' 

// i.e displayName=user.dispalyName

// name=fullName.firstName

console.log(displayName, name);