Named Parameters

Ordered parameters can make the code harder to read and refactor.

class Customer {
    constructor(firstName, lastName, email, phoneNumber) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
        this.phoneNumber = phoneNumber;
    }
}
​
new Customer('Foo', null, null, '123');

Unluckily, named parameters do not exist in JavaScript but there is a native workaround thanks to destructuring.

Named Parameters with one parameter

class Customer {
    constructor(args) {
        this.firstName = args.firstName;
        this.lastName = args.lastName;
        this.email = args.email;
        this.phoneNumber = args.phoneNumber;
    }
}
​
new Customer({
    firstName: 'Foo',
    phoneNumber: '123'
});

But this is not very IDE-friendly and without reading the content of the constructor, there's no way to know what are the expected parameters.

Destructuring

The destructuring can be used in the constructor's (or any other function) parameters description.

class Customer {
    constructor({firstName, lastName, email, phoneNumber = null} = {}) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
        this.phoneNumber = phoneNumber;
    }
}

Which is a shorthand for:

class Customer {
    constructor(args = {}) {
    
        const {firstName, lastName, email, phoneNumber = null} = args;
    
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
        this.phoneNumber = phoneNumber;
    }
}

Recycling

For simple objects, this constructor can be used as is without having to implement factories for handling copy or deserialization.

const customer = new Customer({firstName: 'Foo'});
​
const customerFromJson = new Customer(JSON.parse(data));
​
const customerCopy = new Customer(customer);