Destructuring Assignment In A Function Parameter
Tags: javascript, webdev
Published: 2020-12-07 17:08:11

Have you ever passed an argument as a `null` or `undefined` in a function? Since ES2015 (aka ES6) **you don’t have to**. You can use JavaScript destructuring.

## Use Case

We all have this Utils.js file in our projects where we have all kinds of functions that will be used all over the project. Imagine you have a To-Do app and one of those functions was addTodoItem and you had to call this function in different places.

Function declaration would look like this:
```javascript
function addTodoItem(title, description, dueDate) {
  // Your code here
}
```

Before calling the function, see the characteristics for each parameter:


- Title => required.
- Description => !required.
- DueDate => !required.

Let’s add a few items to the list now.

```javascript
addTodoItem('Shopping List', 'eggs, milk', '30-11-2020')
> { title: 'Shopping List', description: 'eggs, milk', dueDate: '30-11-2020' }
addTodoItem('Call Mom')
> { title: 'Call Mom' }
addTodoItem('Pay Bills', undefined, '01-12-2020')
> { title: 'Pay Bills', dueDate: '01-12-2020' }
```

If we pay attention to the last example, we can see that on the first day of the month I need to pay my bills. 🤣

Jokes aside, we see that I had to pass the second value as `undefined` because the function is expecting the description as the second parameter.

For this specific example, if I wanted to pass a dueDate, first I would have to check whether the description is `undefined` or not before I call the addTodoItem function.

Here is where using destructuring will be very helpful.

This is how the addTodoItem would look now. 👇

```javascript
function addTodoItem({title, description, dueDate}) {
  // Your code here
}
```
Let’s add again the same items as before.


```javascript
addTodoItem({ title: 'Shopping List', description: 'eggs, milk', dueDate: '30-11-2020' })
> { title: 'Shopping List', description: 'eggs, milk', dueDate: '30-11-2020' }
addTodoItem({ title: 'Call Mom' })
> { title: 'Call Mom' }
addTodoItem({ title: 'Pay Bills', dueDate: '01-12-2020' })
> { title: 'Pay Bills', dueDate: '01-12-2020' }
```
If you pay attention to the last item added, you’ll see that there was no need on adding the `undefined` for the description. Just title and dueDate.

## Bonus!
There is more: not only do you not need to pass `undefined` anymore, but you can even change the order of how you pass the arguments and it will still work.

```javascript
addTodoItem({ description: 'eggs, milk', dueDate: '30-11-2020', title: 'Shopping List' })
> { title: 'Shopping List', description: 'eggs, milk', dueDate: '30-11-2020' }
addTodoItem({ title: 'Call Mom' })
> { title: 'Call Mom' }
addTodoItem({ dueDate: '01-12-2020', title: 'Pay Bills' })
> { title: 'Pay Bills', dueDate: '01-12-2020' }
```

## Conclusion

That’s it! We saw how to use destructuring when declaring a function and how to call that function and provide the arguments. 

Remember that you can get rid of the `undefined` or `null` since the order of the arguments doesn’t matter.

PS. Remember to pay your bills. 🤣

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