In this blog, you will learn to assign properties of an Object to individual Variables.

Suppose you have a person object that has two properties called firstName and lastName.

let person = {
    firstName : "Kenil",
    lastName : "Kanani"
}

Before Es6 was introduced, if you have to perform object destructuring then you do like this,

let firstName = person.firstName;
let lastName = person.lastName;

Es6 introduces object destructuring syntax, an alternative way to assign properties of an object to a variable.

// Syntax

let { property1: variable1, property2: variable2 } = object;

Consider the person object mentioned above,

let { firstName: f_Name, lastName: l_Name } = person

In the above-mentioned example, the firstName property present in the person was assigned to the variable called f_Name and lastName property present in the person was assigned to the variable l_Name .

The identifier before the colon (:) is the property of the object and the identifier after the colon is variable.

If the variable has the same name as the property of the object then you can use even more short syntax,

let { firstName, lastName } = person;

You can do declaration and initialisation separately,

let firstName, lastName;
({ firstName, lastName } = person);

If you don’t use the parentheses, the JavaScript engine will interpret the left-hand side as a block and throw a syntax error.

When you assign a property that does not exist to a variable using the object destructuring, the variable is set to undefined. For example:

let { firstName, lastName, middleName } = person;
console.log(middleName); // undefined

Setting default values

You can assign a default value to the variable when the property of an object doesn’t exist. For example:

let person = {
    firstName: 'Kenil',
    lastName: 'Kanani',
    currentAge: 19
};

let { firstName, lastName, middleName = '', currentAge: age = 18 } = person;

console.log(middleName); // ''
console.log(age); // 19

In this example, we assign an empty string to the middleName variable when the person object doesn’t have the middleName property.

Also, we assign the currentAge property to the age variable with the default value of 18.

However, when the person object does have the middleName property, the assignment works as usual:

let person = {
    firstName: 'Kenil',
    lastName: 'Kanani',
    middleName: 'Hello',
    currentAge: 19
};

let { firstName,  lastName, middleName = '', currentAge: age = 18 } = person;

console.log(middleName); // 'Hello'
console.log(age); // 19

Destructuring a null object

A function may return an object or null in some situations. For example:

function getPerson() {
    return null;
}

And you use the object destructuring assignment:

let { firstName, lastName } = getPerson();

console.log(firstName, lastName);

The code will throw a TypeError:

TypeError: Cannot destructure property 'firstName' of 'getPerson(...)' as it is null.

To avoid this, you can use the OR operator (||) to fallback the null object to an empty object:

let { firstName, lastName } = getPerson() || {};

Now, no error will occur. And the firstName and lastName will be undefined.

Nested object destructuring

Assume you have person object is shown below,

const person = {
    name : 'Ken!l',
    age : 19,
    address : {
        street : "Katargam , Surat",
        city : "Surat",
        state : "Gujarat"
    }
}

The following statement destructures the properties of the nested address object into individual variables:

let {
    address:{
        street,
        city,
        state
    }
} = person;

Destructuring function arguments

It’s possible to destructure the object argument passed into the function like this:

let display = ({firstName, lastName}) => console.log(`${firstName} ${lastName}`);

let person = {
    firstName: 'Kenil',
    lastName: 'Kanani'
};

display(person);