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Sakib Ahmed
Sakib Ahmed

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Tips: Object Destructuring in JavaScript ES6

Suppose you have a person object with TWO prperties:

let person = {
   firstName: 'Devv',
   lastName: 'Sakib'
}
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Before ES6, when you want to assign the variables to the properties of the person object, you typically do like this:

let firstName = person.firstName
let lastName = person.lastName
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But but but, ES6 make it more easier! There are an alternative way to assign properties of an object. Let's see

let { firstName: fName, lastName: lName } = person
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Here, firstName and lastName prop are assgined to fName and lName variables.

Syntax:

let { 
    property: variable, 
    property: variable 
    } = object
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Notice that the property name is always on the left whether it is object literal or object destructuring syntax.

TO KNOW: If the variables have the same name as the properies of the object, you can make the code more concise as follows:

let { firstName, lastName } = person

console.log(firstName) // "Sakib"
console.log(lastName) // "Smith"
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In this examples, we declared two variables firstName and lastName, and assigned the properties of the object to the variables in the same statement.

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

Example:

let { firstName, lastName, middleName } = person

console.log(firstName) // "Sakib"
console.log(lastName) // "Smith"
console.log(middleName) // undefined
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The middleName property does not exist in the person object, that's why middleName is undefined

Default Values

You are able to assign a default value of the variable when the property of an object doesn't exist.

Example:

let person = {
   firstName: 'Devv',
   lastName: 'Sakib'
}

let { 
    firstName, 
    lastName, 
    middleName = ''
    } = person

console.log(middleName) // ''
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In this example, we assigned empty string to the middleName variable when the person object doesn't have the middleName property.

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

Example:

let person = {
   firstName: 'Devv',
   lastName: 'Sakib',
   middleName: 'IDK'
}

let { 
    firstName, 
    lastName, 
    middleName = ''
    } = person

console.log(middleName) // 'IDK'
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Destructuring a null object

If you know, a function may return an object or null in some case.

const person = () => {
   return null
}

let { fname } = person()

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But you can't destructure an null object. The code will throw a TypeError

TypeError: Cannot destructure property 'fname' of 'person()' as it is null.
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To solve this, you can use the OR(||) operator to fallback the null object t an empty object.

let { fname } = person() || {}
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Now, fname will be undefined

There are so many destructuring, will write later. See yaa

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