Victor Adeshile

Destructuring Array, Objects, and Function Params in JavaScript

Destructuring Array, Objects, and Function Params in JavaScript

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Victor Adeshile

Published on Jan 29, 2021

6 min read

Destructing is a method of extracting some data from an Array, Object or function Parameters Below is an example of how an Array can be destructured.

const names = ['Victor', 'Jade', 'Edidiong', 'Tina'];

By design, we know that each element of an array has an index identifier starting from 0 to the end of the array. Arrays are also ordered list of element, so the order matters also while destructuring.

const [Winner, second, ...everyoneElse] = names;

// if we call the variable Winner, it stores the first element of the array 'Victor'.
// Winner
// OutPut: "Victor"
// second
// OutPut: "Jade"
// everyoneElse
// OutPut: ["Edidiong", "Tina"]

The names Array is not tampered with in any way, we have only created a list of variables for the elements found in the names Array.

As seen in the code above, we used the Rest operator (...everyoneElse) to categorize the remaining elements in the name array. This makes us get the remaining elements as a new array in the variable name everyoneElse.

Destructuring of Arrays isn't really common in programming, what's more, common is destructuring of Objects.

Below we would learn how to destructure an Object and its common use.

const subjectScores = {
    english: 98,
    math: 90,
    socialStudies: 95,
    elective: 60

If we had to access each element before, we would do the following;

const english = subjectScores.english;

// Now if we called english, would get 98.

If we had way more data to pull out and use for a specific purpose, it would be crazy to have to repeat this pattern, for this sake, we can use destructuring.

const {math, elective, ...allOthers } = subjectScores;

just like we did with arrays, it's easy to also destructure an Object, and the same would apply this case.

How do we rename any of the key in the subjectScores Object?

To do this, find the key that we want to rename and then, assign a new name to it. This would nake the previous name unusable.

const {elective: electiveStudies, english} = subjectScores;

Now that we have renamed the key "elective" to "electiveStudies", if we call elective, we would get the following error "Uncaught ReferenceError: elective is not defined".

But if we call english, we would still get the output 98, and if we call the new name electiveStudies, OutPut: 60.

Another very common use case is to use default params with Destructuring.

const arry = {
    // name: 'James',
    occupation: 'Programmer',
    bankSum: 700,
        return 700 * num / 100;

// If we called we would get 'James'

But if we destructure like we did below and assigned a default Param to name like seen below;

const {name: named = 'Goblin' } = arry;

The name still remains 'James' because we have it assigned already in the array and that takes precedence.

But If we remove the name Property and then destructure again with the same example, we will access the property using the new name property.


const arrys = {
    occupation: 'Programmer',
    bankSum: 700,
        return 700 * num / 100;


const {name: namedd = 'Shawl' } = arrys;

const fullName = function ({occupation, bankSum}) {
    return `${occupation}, ${bankSum}`;

Now, namedd will OutPut 'Shawl' as expected.

Destructuring Params in Functions

Let's create an Object for example;

const users = {
    name: 'Victor',
    isAdmin: false,
    email: '',
    dob: '20/01,1901',
    ethnicity: 'Black'

Now, we would create a Function that takes in the arguments or properties of the Object Above.

const callUsersDet = function({email, dob, isAdmin}){
return `Users email is: ${email}, born on the: ${dob}, and is Admin privilege is ${isAdmin}.`;

Whenever we call the callUsersDetails function, it is expecting us to pass in Object that has all these properties that are housed in the users Object, to do this, we would say; callUsersDetails(users);

This would call return the following output; "Users email is: , born on the: 20/01,1901, and is Admin privilege is false."

I hope this helps clarify what is going on.

Destructuring really is very simple if understood its use cases, I hope I've been able to clarify a little about the Topic.

If you found this write up helpful, pls share it with any friend learning JavaScript Basics to help them also get ahead.

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